British Prime Minister Theresa May met Jordan's King Abdullah II Monday at the start of a three-day trip to the kingdom and Saudi Arabia focused on security and post-Brexit trade efforts.
In Jordan, May is expected to announce that British military trainers will be sent to help the country's air force fight the Islamic State group.
She will visit Saudi Arabia on Tuesday and Wednesday for talks focused on trade and investment as Britain begins the process of leaving the European Union.
Jordan's official news agency Petra reported that May met the king shortly after arrival to discuss "military cooperation between both countries", "the Syrian crisis and peace process", and "counterterrorism efforts".
They visited the headquarters of Jordan's Rapid Response Forces, where May was told about the counterterrorism unit's missions and training programmes as part of the cooperation between both countries, it said.
May said before leaving Britain that it was "clearly in the UK's security and prosperity interests to support Jordan and Saudi Arabia".
May will set out a package of measures to boost cooperation between British forces and the Royal Jordanian Air Force, which along with Britain is part of the US-led coalition bombing IS in Iraq and Syria.
It will include training carried out in Jordan and Britain to help the RJAF "improve its capability" to carry out air strikes against IS, she said.
"To tackle the threats we face from terrorism and from geopolitical instability, we must meet them at their source," May said, describing Jordan as "on the frontline of multiple regional crises".
- 'Keep British people safe' -
In the wake of last month's deadly attack on the British parliament, she said that by working with countries such as Jordan "we are helping to keep British people safe".
May said she would also discuss ways to help Jordan host a massive influx of refugees from the war in neighbouring Syria.
In Riyadh, May will focus on trade, saying ahead of her trip that there is "immense potential for Saudi investment to provide a boost to the British economy".
Britain is looking to strike new trade deals after May last week formally activated Article 50 of the Lisbon Treaty, starting a two-year countdown for quitting the European Union.
Qatar announced plans last month to invest £5 billion ($6.23 billion/5.8 billion euros) in Britain within five years.
Saudi Arabia is also looking at boosting its foreign investments as part of a long-term plan to diversify its economy and reduce its dependence on oil revenues.
May attended a Gulf Arab summit in December in Bahrain, where she became the first woman and first British leader to address a summit of the six-nation Gulf Cooperation Council.
At the time, she said Britain would help "push back" against Iran -- a key rival of Gulf Arab nations -- and said she hoped to eventually agree an ambitious trade agreement with GCC countries.
Britain is a major arms supplier to Saudi Arabia, and has faced repeated calls to suspend sales over Riyadh's military intervention in neighbouring Yemen.
- Calls to end arms sales -
A Saudi-led coalition has been carrying out a bombing campaign in support of Yemen's internationally recognised government against Iran-backed Huthi rebels who have seized large parts of the Arabian Peninsula country.
Since the start of the campaign two years ago, more than 7,700 civilians have been killed and a further 40,000 wounded, according to the United Nations.
Seven million Yemenis now face starvation, the UN says.
Rights groups including Amnesty International and Human Rights Watch have been among organisations calling for an end to arms sales from Britain and the United States to Saudi Arabia over the coalition's actions in Yemen.
Asked if May would be raising the issue of Yemen during the visit, her spokesman said it was "not on the agenda".
"Discussions with Saudi Arabia will be mostly focused on defence and prosperity issues," the spokesman said.
"The purpose of this visit... is to look at regional challenges in the area, discuss defence and security cooperation. A large part of it will be looking at future trading and business relationships between the UK and Saudi Arabia."
On Sunday, Britain apologised after an egg was thrown at Saudi General Ahmed Assiri, the spokesman for the coalition, during a recent visit to London.
An anti-war activist last week attempted a citizen's arrest of Assiri, before another threw an egg that hit the spokesman in the back.