The US Secretary of State says Syria's use of chemical weapons crosses a "global red line."
John Kerry has arrived in Britain to gain support for military action against the country.
His mission comes as the Syrian President once again warned he'll retaliate if the country is attacked over the issue of chemical weapons.
Survivors of the attack in Damascus are still struggling to recover three weeks after it happened.
In a rare insight into life there ITV News has talked to some of those in Zamalka, a rebel-held suburb.
From Damascus ITV News International Editor Bill Neely reports:
President Assad has suggested there would be retaliation by those aligned with him for any attack on Syria.
In an interview with CBS News, Assad also said he is very concerned that an attack on Syria would degrade his military and tip the balance in the conflict.
Syrian president Bashar Al-Assad has denied he was behind the chemical weapons attack in Damascus, according to CBS News.
He told the CBS Face the Nation programme: "There has been no evidence that I used chemical weapons against my own people."
In an interview in Damascus, Assad said there was no conclusive evidence of a chemical attack.
U.S. Secretary of State John Kerry said on Sunday the United States did not rule out the possibility of returning to the United Nations Security Council to secure a resolution on Syria once U.N. inspectors complete their report.
Speaking at a news conference in Paris, Kerry said President Barack Obama had yet to make a decision on the issue.
"The end of this civil war is going to require a political solution.
"There is no military solution. What the US is seeking - not alone, but together with others - is to enforce the standard with respect to the use of chemical weapons," he said.
"We are not seeking to become engaged in, or party to, Syria's civil war", he said.
US President Barack Obama will give six television news interviews to push his case for taking military action against Syria, ahead of the pivotal vote in Congress.
Mr Obama will record interviews with PBS, CNN, Fox and three network news channels on Monday afternoon, with the exchanges airing in the evening's broadcasts.
The president will make his case for pursuing military strikes in response to an alleged chemical attack by the Assad regime in a prime time speech the following day.
France's President Francois Hollande has said it is likely that the UN Inspectors' report on Syria will be released by the end of the week.
Secretary of State John Kerry has said that President Obama has made no decision on waiting for the UN inspectors report.
Kerry said: "The President of the United States has made no decision I will return to Washington and obviously this will be a point of discussion but we take that decision under advisement.
"But the President has taken no decision this respect of what he may or may not do."
U.S. Secretary of State John Kerry has welcomed a European Union statement on Saturday that said there appeared to be strong evidence that the Syrian government carried out a chemical attack on civilians last month.
Speaking after meeting EU foreign ministers in the Lithuanian capital Vilnius, Mr Kerry said: "We are very grateful for the statement that came out of the meeting today with respect to Syria -a strong statement about the need for accountability."