Syria Conflict: How The Key Countries Line Up

Russia's military intervention in Syria has added another potent force to an already volatile mix. Here, we look at the contribution and motivation of some of the major forces.

Support for the Syrian government

:: Russia

Russia supports the Bashar al Assad government and has supplied its forces with arms as part of a business contract signed before the uprising began.

Crucially, Russia's Tartus naval depot is based in Syria - the only one outside the former Soviet Union.

Before Wednesday's intervention, Russia had reportedly sent military advisers to train pro-Assad soldiers, using Russian-made weapons.

Some reports have even suggested that Russia is keeping the Syrian economy afloat by flying in plane-loads of banknotes.

Recently Russia has intensified its military activity inside Syria.

It has supplied armoured vehicles, electronic warfare systems and powerful weapons including guided bombs for planes.

There are currently 32 Russian warplanes based near the Syrian port city of Latakia, guarded by 1,700 Russian marines.

On 30 September, Russia's upper parliamentary house granted Vladimir Putin permission to begin military action in Syria.

Officials in Russia say that, for the time being, the action will be restricted to airstrikes, and not troops on the ground.

Mr Putin says that the strikes are preemptive attacks on Islamic State terrorists, in a bid to stop them advancing into Russia.

At least 30 strikes were conducted in the hours after Mr Putin was granted permission to attack.

The Kremlin said 12 IS targets were hit, including a command centre.

However, US officials say the strikes did not hit areas occupied by IS, but rather Syrian rebels, some of whom were trained by the CIA.

According to The Syrian National Council - a group opposed to Mr Assad - 36 civilians, including five children, were killed by the first wave of strikes.

:: Iran

Iran and Syria are close allies.

The former has been the main backer of Mr Assad's regime, since well before the conflict.

Iran's support of Mr Assad may stem partly from the fact that the Syrian city of Zabadani is of crucial importance to Iran.

The city has served as the Iranian Revolutionary Guard Corps's logistical hub for supplying Hezbollah.

And Iranian-backed Hezbollah guerrillas have been battling alongside Syrian government forces.

Support for the Syrian regime has reportedly included combat troops and £6bn of financial support.

There have been increasing reports of Iranian military support for Mr Assad.

Iran has warned that any foreign intervention risks sparking a regional war.

:: Other parties

Venezuela, North Korea, Iraq, China and Lebanon have all reportedly offered support for the Assad regime, though the degree to which each has contributed is unclear.

Support for the Opposition

:: Britain

The UK opposes the Assad regime on humanitarian grounds, citing the use of chemical weapons as a reason to intervene.

However, after the campaign in Libya in 2011, NATO said it had no intention of taking military action in Syria.

Despite this, according to Reuters, the prospect of British special forces entering Syria on the ground was growing in June 2012.

It followed unconfirmed reports from an Israeli website that SAS Commandos were engaging in covert operations within Syrian territory.

This was never confirmed.

In the same month, Sky News reported how the UK provided opposition forces with £5m of non-lethal military aid.

This included funds for communications equipment and medical supplies.

Sky News also revealed that the UK provided intelligence support from its Cyprus bases, reporting Syrian military movements to Turkish officials.

Details of these movements were then passed on to the Free Syrian Army, a group of defected Syrian Armed Forces soldiers, who oppose the regime.

On 29 August, 2013, a Commons vote was held to decide whether the UK would join the US in militant action, based on the use Mr Assad's use of chemical weapons.

The motion was defeated by 285 votes to 272, despite the support of PM David Cameron.

In July, it emerged that British pilots embedded with the US and Canadian troops, had been conducting strikes against IS in Syria, despite the vote.

Defence Secretary Michael Fallon admitted a "handful" of British pilots who were embedded with American forces had taken part.

This was acceptable, Mr Fallon said, as the US had full approval for military action.

On 21 August, three IS fighters, including two British men, were targeted and killed in Raqqa , Syria by an RAF MQ-9 Reaper strike.

Mr Cameron said one of the British nationals had been plotting attacks in the UK.

Another British national was killed in a separate air strike by US forces in Raqqa on 24 August.

:: United States

The US has been one of the strongest advocates of military action against the Syrian regime.

Barack Obama has accused Mr al Assad of using chemical weapons.

In June 2012, the CIA was reported to be involved in covert operations along the Turkish-Syrian border.

According to these reports, CIA agents investigated rebel groups and then recommended which groups to give aid to.

It was reported that agents also helped rebel forces to develop supply routes, as well as distributing assault rifles and anti-tank rocket launchers.

In September 2013, Mr Obama sought Congressional support for military action but postponed the vote when Syria said it would give up its chemical stockpile.

In April 2013, the government vowed to double non-lethal aid to rebels - to $250m (£165m).

On 13 June, Mr Obama reportedly approved providing lethal arms to the Supreme Military Council.

The SMC is a rebel command structure that includes representatives from most major rebel groups, excluding Islamic State.

In September last year, the US began surveillance missions on IS in Syria.

Mr Obama said: "I have made it clear that we will hunt down terrorists who threaten our country, wherever they are. That means I will not hesitate to take action against ISIL in Syria."

On September 22, 2014, the US, Bahrain, Jordan, Qatar, Saudi Arabia, and the UAE began to strike IS targets in Syria.

According to sources, speaking to Reuters, at least 50 civilians have been killed in Syria by US-led airstrikes.

:: France

In September 2013, President François Hollande said the country was ready to begin supplying lethal aid to the Free Syrian Army.

Earlier this week, France upped the ante and carried out its first airstrikes against IS in Syria.

By doing so, it expanded its aerial campaign against IS in Iraq - which it began a year ago.

Justifying the attacks, Mr Hollande said: "We will strike whenever our national security is at stake."

The first wave of airstrikes reportedly destroyed an IS training camp, killing at least 30 people.

Among those killed, according to the British-based Syrian Observatory for Human Rights, were several teenage IS fighters from Arab states.

France has also confirmed it is now investigating Mr Assad over alleged crimes against humanity.

The investigation is further examining claims of torture and kidnapping by Mr Assad's forces.

:: Turkey

Turkey has previously enjoyed friendly relations with Syria.

But the relationship has deteriorated and Turkey has condemned Mr Assad over his use of violence against citizens.

Turkey has now trained defectors of the Syrian Army on its territory, and in July 2011 a group of them announced the birth of the Free Syrian Army.

The country offers members of the Free Syrian Army shelter and a base of operation and has provided rebels with arms.

Tensions between Turkey and Syria heightened after regime forces shot down a Turkish fighter jet in June 2012.

Earlier this summer, there were unsubstantiated reports of a planned joint Jordanian/Turkish invasion of Syria.

The reports stated that several meetings had been held in Ankara and preparations made.

While opposing Mr Assad, the Turkish government has been accused of maintaining a "Jihadi highway".

The highway allows IS militants, some from Britain, to cross into Syria to fight with the terror group.

:: Saudi Arabia

Saudi Arabia has been a rival of the Syrian government for years.

According to reports, it has financed the supply of infantry weapons, such as Yugoslav-made recoilless guns, to rebels.

Mr Assad accused Saudi Arabia of being the major supporter of terrorists and "leading the most extensive operation of direct sabotage against all the Arab world".

:: Qatar

Qatar had funded rebels in Syria to the tune of up to £2bn, according to a report in the Financial Times.

The Stockholm International Peace Research Institute said the country had sent the most weapons to Syria out of all countries.

According to the Institute, it has sent 70 cargo flights, packed with weapons, into Turkey between April 2012 and March 2013.

In addition, Qatar reportedly operates a training base in its territory, in conjunction with the CIA, who run the training.

The camp reportedly trains about 1,200 rebel soldiers a year on three week-long courses.

:: Jordan

Jordan is supporting the US-led bombing of IS in Syria, amid threats from the group that it will overthrow the country's monarchy after it takes Baghdad.

Jihadist troops have retaliated by firing into Jordan and there has been increased sniping at the border.

On Christmas Eve last year, a Jordanian fighter jet was shot down over Syria.

Its pilot Muath Al-Kasasbeh was captured and then burned alive in a cage - the video of the execution posted on YouTube.

In response, Jordan executed terrorists, Sajida al-Rishawi and Ziad al-Karbouli - and took the lead in the anti-IS airstrikes.