Red-stained hands of anti-war protesters waved for hours on Wednesday behind Obama administration officials urging lawmakers to authorise military strikes against Syria.

Demonstrators said the red represented the blood that would be on Secretary of State John Kerry's hands if Congress approves military attacks in retaliation for Syria's suspected use of chemical weapons against its own people.

Secretary of State John Kerry said Wednesday the 'world is watching' as he pressed the administration's case for military action in Syria.

The silent demonstration, led by the anti-war group Code Pink, involved about 10 activists, but the whole world was indeed watching because the protest took place during a televised congressional hearing.