BEIRUT — International efforts to pressure Syria intensified Monday, as the UN special envoy, Kofi Annan, began negotiations in Damascus and the chairman of the US Joint Chiefs of Staff warned that continued atrocities could make military intervention more likely.
Annan traveled to Syria seeking to salvage his peace plan, which appeared more precarious than ever after the massacre of at least 108 villagers in the Houla area of central Syria.
He urged the government to hold to its commitment in March to honor the six-point plan, which included not only a cease-fire, but also political dialogue with the opposition and freedom for Syrians to demonstrate.
“I urge the government to take bold steps to signal that it is serious in its intention to resolve this crisis peacefully, and for everyone involved to help create the right context for a credible political process,’’ Annan said.
Creating the right climate for progress was the responsibility of not only the government but “everyone with a gun,’’ he added.
Questions about the viability of the plan were thrown into sharp relief by the massacre in the villages that constitute Houla, near Homs, on Friday, whose victims included 49 children and 34 women by the United Nations’ count.
The UN Security Council on Sunday unanimously condemned the massacre and, although not assigning blame, censured the Syrian government for using heavy artillery against the civilian population. It was the toughest language Russia has supported about the conflict in Syria, its close ally.
The Russian foreign minister, Sergey V. Lavrov, said that although terrorists among the opposition were causing some of the violence, the Syrian government was responsible for most of it.
After a meeting about Syria with his British counterpart, William Hague, the two agreed that the main priority was to fully implement the peace plan.
The aftermath of the killings continued to reverberate inside Syria on Monday. Shops — including the famous Hamadiyah bazaar of Damascus — stayed shut as part of an opposition-led call to observe three days of mourning, according to opposition activists and residents.
Damascus has been a bastion of government support. The activists said government agents forced some stores to reopen, particularly in the nut and candy bazaar, by prying open their metal shutters.
Annan, the envoy of both the United Nations and the Arab League and a former UN secretary-general, arrived with a new mandate from the Security Council — including Russia, which had usually blocked action against its ally in Damascus — to implement his plan.
Annan met Monday with Walid al-Moallem, the Syrian foreign minister, and is to see President Bashar Assad on Tuesday. He will also meet with a variety of other people on the trip, which was scheduled before the massacre, including opposition figures from within Syria.
From the beginning, the peace plan has been given slim chances of success.
But it was seen as an acceptable means to try to bridge the differences over Syria between the West and the Arab states on one side and Russia, China, and Iran on the other.
Some analysts have called it an international stalling measure, because the Western appetite for military intervention in the conflict is low even in the absence of Russian opposition.
In Washington, General Martin E. Dempsey, the chairman of the Joint Chiefs of Staff, called the massacre in Syria “horrific’’ and “atrocious’’ and said that he was prepared with military options in Syria should they be requested by the White House. But he otherwise spoke cautiously about any US intervention by force.
“There is always a military option, but that military option should always be wielded carefully,’’ Dempsey said on Fox News. “Because one thing we’ve learned about war, I have learned personally about war, is that it has a dynamic all its own; it takes on a life of its own.’’
Nonetheless, he said, “it may come to a point with Syria because of the atrocities.’’
White House officials said Monday that Dempsey’s television appearances were not a coordinated administration response to Syria but had been previously planned as part of the administration’s commemoration of Memorial Day.
In recent days, the Obama administration has come under intensified criticism by some in Congress and by Republican presidential front-runner, Mitt Romney, who accused President Obama of not doing enough to help the Syrian opposition.
In his Moscow comments, Lavrov repeated Russia’s position that it was not tied to Assad staying in power, rather that the Syrians pilot their own political transition.
“For us, the main thing is to put an end to the violence among civilians and to provide for political dialogue under which the Syrians themselves decide on the sovereignty of their country,’’ he said.