Syria Allows UN Visit To 'Chemical Attack' Site

United Nations weapons experts will investigate the site of an alleged chemical weapons attack in Syria on Monday.

UN Secretary-General Ban Ki-moon said Syria has promised to observe a ceasefire at the site in the eastern suburbs of Damascus while the team begins "on-site fact-finding activities".

The 20-strong team arrived in Damascus three days before a mass poisoning killed several hundred people on Wednesday.

The announcement comes after Syria warned the US against taking military action against the regime, saying it would "create a ball of fire that will inflame the Middle East".

British Foreign Secretary William Hague said that evidence of a chemical weapons attack could have already been destroyed and "we have to be realistic now about what the UN team can achieve".

He said: "There is a lot of evidence already and it all points in one direction", pointing the finger at President Bashar al Assad's forces over the alleged gas attack.

"We cannot in the 21st century allow the idea that chemical weapons can be used with impunity, that people can be killed in this way, and there are no consequences for it," he said.

"And so we believe it's very important that there is a strong response and that dictators - whether they are Assad or other people who might slaughter their own people or attack people of any other country - know that the use of chemical weapons is to cross a line, and the world will respond when that line is crossed."

He refused to discuss "what options were on the table" for Western leaders.

But he said the UK was in talks with the US and other countries and stressed it was important "to act within international law and to have widespread international support for making sure chemical weapons can't be used with impunity."

Russia has warned the West that military action against the Syrian regime would be a "tragic mistake".

Earlier, Prime Minister David Cameron and President Barack Obama said they were "gravely concerned" about signs that an alleged chemical attack had taken place in Syria.

The two leaders spoke with Canadian Prime Minister Stephen Harper by telephone last night as calls increased for UN investigators to be allowed access to the site.

Mr Cameron also spoke to France's President Francois Hollande on Sunday to discuss the crisis in Syria.

French Foreign Minister Laurent Fabius told a Jerusalem news conference there was "no doubt" the Damascus regime was behind the suspected poison attack.

The US President and his top advisers are continuing to explore options for responding to the attack, with the White House saying there is "very little doubt" the regime has used chemical weapons against its citizens.

In remarks released by Syria's official SANA news agency, Syrian Information Minister Omran Zoabi said that any US-led military action would be "no picnic".

"US military intervention will create a very serious fall-out and a ball of fire that will inflame the Middle East," Mr Zoabi said.

Meanwhile, the al Qaeda-linked Syrian jihadist group Al Nusra Front has also vowed to carry out strikes against villages from Assad's community as revenge for the alleged chemical attacks.

Damascus has strongly denied it carried out the attack, instead blaming the rebels.