BEIRUT – France raised the prospect of military intervention in Syria on Wednesday, saying the U.N. should consider harsher measures if an international peace plan that has been shaken by violence ultimately collapses.

The statement reflects mounting international frustration with daily attacks that have kept a cease-fire between troops loyal to President Bashar Assad and armed rebels seeking to oust him from taking hold.

Activists said government troops killed at least 29 civilians Wednesday, including 12 killed in shelling in the central city of Hama.

Rebels attacked elsewhere, killing at least four security personnel.

French Foreign Minister Alain Juppe said France had discussed invoking Chapter 7 of the U.N. Charter, which can be enforced militarily, with other world powers. U.S. Secretary of State Hillary Clinton said last week the United Nations should move toward such a step to allow for measures like travel and financial sanctions and an arms embargo. She didn’t mention military action. The U.S. has for more than a year opposed the further militarization of the situation.

Any such move, however, would likely be blocked by Russia and China, which have twice used their vetoes as permanent Council members to protect Syria from condemnation and remain opposed to military intervention. Western powers, too, don’t appear interested in sending forces to another Middle East nation in turmoil.

Instead, all parties have backed a peace plan brokered by envoy Kofi Annan that calls for a cease-fire to allow for dialogue between the regime and the opposition on a political solution to the 13-month-old conflict which has killed more than 9,000 people.

That plan, however, has been troubled from the start. Syria has failed to enact key parts of the plan, like withdrawing its forces from cities, and its troops have attacked opposition areas, killing scores of civilians since the truce was to begin on April 12. Rebel fighters, too, have attacked military checkpoints and convoys.

In Paris on Wednesday, Juppe said the plan was “severely compromised” but must go ahead.

“We think this mediation should be given a chance,” he said after a meeting with Syrian dissidents. He called for the full contingent of 300 observers authorized by the Security Council to be deployed in Syria in 15 days and said Annan’s report on the cease-fire scheduled for May 5 will be a “moment of truth” on whether mediation can solve the conflict.

“We cannot allow ourselves to be defied by the current regime,” he said.