PARIS - Secretary of State Hillary Rodham Clinton called Thursday for the U.N. Security Council to adopt an arms embargo and other tough measures against Syria to try to halt 13 months of bloodshed, but she acknowledged that such diplomatic actions would likely be vetoed.

Clinton's comments to Western and Arab diplomats from the so-called "Friends of Syria" group came as the head of the United Nations accused Syrian President Bashar al-Assad of failing to honor a peace plan that went into effect a week ago.

In a transcript of her remarks on the State Department's website, Clinton stopped short of calling for outside military intervention in Syria - something there is little to no foreign appetite for - but said it was time to impose more consequential measures on Assad's regime.

"We have to keep Assad off balance by leaving options on the table," she told the gathering of 16 top diplomats.

Clinton's address suggested the United States wanted the "Friends of Syria" group to more actively consider contingency plans if the peace plan by U.N. and Arab League envoy Kofi Annan fell apart. Although U.S. policy has amounted to an acknowledgment that Assad is unlikely to be dislodged, the U.N. resolution Clinton seeks could strengthen Syrian rebels fighting his regime.

"We need to start moving very vigorously in the Security Council for a Chapter 7 sanctions resolution, including travel, financial sanctions, an arms embargo, and the pressure that that will give us on the regime to push for compliance with Kofi Annan's six-point plan," Clinton said, referring to a resolution under the U.N. Charter that would be militarily enforceable.

Clinton said she had laid out the case for Security Council action earlier Thursday to Russian Foreign Minister Sergey Lavrov, whom she said "has recognized that we are not in a static situation but a deteriorating one."

At the Paris meeting, French Foreign Minister Alain Juppe said the "Friends of Syria" group believes Annan's plan is the "last chance" for Syria to avoid civil war. But he didn't rule out the possibility of tougher action at the Security Council, including "in the direction that Madame Clinton indicated."