How should the US react to a 'moral obscenity' in Syria?

Kerry said the US would take "an informed decision" on how to respond to the use of chemical weapons

US Secretary of State John Kerry has denounced the Syrian government for attacking its own people with chemical weapons in a highly-charged, emotional, statement.

He appeared to be preparing the ground for military action, while giving away no details of what will be done.

Mr Kerry said what happened was a moral obscenity that should shock the world and offend "our basic sense of humanity".

What else do we learn from his words?

The Obama administration does not need any further evidence that this was a chemical attack and that Syrian President Bashar al-Assad was to blame.

Mr Kerry said the facts were "screaming" out from the pictures, common sense led to one conclusion, and that giving access to the inspectors came "too late to be credible".

But he said that evidence had been collected and would be presented.

Anyone with queasy memories of "dossiers" before the Iraq War will realise that this will come under a lot of scrutiny.

The latest survey indicates 45% of Americans would back an attack on Syria if it had used chemical weapons, but there is still a job to be done persuading the public at home. Mr Kerry said Congress was being consulted.

China and Russia have both warned against an attack, which may mean the US intends to bypass the UN Security Council.

Certainly Mr Kerry did not mention the UN but it would be counter to Mr Obama's instincts not to build wide international support for any action.

All that leaves the question of what will happen, and when.

Mr Kerry left no doubt that action would be taken - he said those who carried out heinous crimes had to be held accountable. He said the president would take "an informed decision" - the same curious formulation used in a Sunday's statement from a White House official.

The administration has deliberately left itself almost no room for manoeuvre - its credibility would now be zero if it failed to take some form of military action.

But there is no sense of a time scale, the scope of any attack, or indeed the limits of its aims.