Pressure is growing to publish detailed evidence of Syria's alleged chemical weapons' use before authorising further intervention in the conflict.
Wary of comparisons with faulty intelligence reports on weapons of mass destruction in Iraq in 2003, senior British MPs said more detail was needed on statements that the banned nerve agent sarin had been identified in tests.
"A greater degree of certainty is required before taking decisive action. We need to have more intelligence, more corroboration," said Richard Ottaway, the British Conservative chairman of the foreign affairs committee.
Central to the claims of chemical weapons' use are positive tests for sarin both by the US Pentagon and British Ministry of Defence scientists at Porton Down.
However, while scientists are said to have confidence in the findings, the quantities involved are "microscopic".
Western leaders hope that the allegations will put new pressure on President Bashar al-Assad to allow a team of UN inspectors to enter Syria and conduct their own sampling of sites in Homs, Damascus and Aleppo.
The regime has invited the team in to conduct tests in Aleppo, where it claims rebels fired poison gas at regime troops, but has refused to grant unconditional access.
In the US, where pressure is mounting to support Syrian rebels fighting the Assad regime more decisively, Senator John McCain, the leading American proponent of intervention, admitted that the chemical weapons evidence "may not be airtight".(© Daily Telegraph, London)