Syrian security forces killed four people as the West ratcheted up pressure for UN Security Council action against Damascus and France slammed China and Russia's 'indecent' opposition to the move.

France, which with other European governments has been circulating a draft resolution at the Security Council for months only to see it blocked by veto-wielding permanent members China and Russia, said it was vital the UN take action over President Bashar al-Assad's deadly crackdown on dissent.

US President Barack Obama told CBS television that Assad had 'missed opportunity after opportunity to present a genuine reform agenda.

Washington had made it clear 'that what we've seen on the part of the Syrian regime has been an unacceptable degree of brutality directed at its people', the US president said.