How strong is US evidence of Syria chemical attack?

John Kerry said evidence of a chemical attack may have been destroyed by shelling

Some US politicians in Congress would like the same right that has been given to British members of Parliament - to vote on whether or not action can be taken against Syria.

One has tweeted that the office of the president can only bypass Congress to make war in the event of a national emergency, although of course it has been done before.

It is likely that President Barack Obama would easily get the authorisation to take military action, but it does mean the media is the only forum to properly test the administration's case.

US Secretary of State John Kerry, in his speech on Monday, and Press Secretary Jay Carney at the White House, make the same argument. They say "common sense" tells the world this was a chemical attack and it was carried out by Syrian President Bashar al-Assad.

'Rocket capacity'

Mr Kerry said: "The reported number of victims, the reported symptoms of those who were killed or injured, the first-hand accounts from humanitarian organisations on the ground, like Doctors Without Borders and the Syria Human Rights Commission, these all strongly indicate that everything these images are already screaming at us is real: that chemical weapons were used in Syria."

He went on: "Moreover, we know that the Syrian regime maintains custody of these chemical weapons.

"We know that the Syrian regime has the capacity to do this with rockets. We know that the regime has been determined to clear the opposition from those very places where the attacks took place."

This is circumstantial and puts a heavy weight on "common sense".

It raises important questions about how strong the evidence needs to be to take such drastic action.

Mr Kerry is of course right that most people will think as he does, simply from watching the TV pictures.

Some, however, will demand much stronger proof, particularly in the wake of the faulty intelligence that was used as a reason to go to war against Iraq.

President Obama has declassified an intelligence report that will be released in the coming days, setting out further analysis.

Members of Congress and British MPs will expect some firm answers - and the public will expect a high degree of scrutiny.