Clinton was speaking at a meeting of NATO ministers in Brussels, where she was asked about action to halt bloodshed in the year-long popular uprising against Assad, who has deployed tanks and troops to try to crush it.

UN-Arab League special envoy Kofi Annan has proposed a peace plan calling for the withdrawal of heavy weapons and troops from Syrian population centers, humanitarian assistance, the release of prisoners and free movement and access for journalists.

“We are at a crucial turning point,” Clinton told a news conference in Brussels. “Either we succeed with...the Annan plan with the help of monitors... or Assad will squander his last chance before additional measures have to be considered. We will continue to increase pressure on Assad.”