BEIRUT, Lebanon — The United Nations Security Council on Sunday unanimously condemned the Syrian government for its role in the massacre of at least 108 villagers, with new details emerging from international observers that appeared to prompt rare Russian cooperation in criticizing its ally in Damascus.

The 15-member Council approved a statement that, while not blaming the Syrian government directly for all the deaths, rebuked it for its use of tanks and artillery against civilians despite agreeing to an April 12 cease-fire.

“The evidence is clear — it is not murky,” Peter Wittig, the German envoy, told reporters after the emergency meeting. “There is a clear government footprint in those killings.”

Syrian government actions not only violate the cease-fire engineered under United Nations auspices, he said, but also jeopardize any effort at peace.

The United Nations says at least 108 people, including 49 children and 34 women, died in Friday’s attacks in the area of Houla, a collection of Sunni villages 15 miles northwest of the central city of Homs. Villagers told the United Nations monitors that at least some of the killings had been committed by “shabiha,” or government thugs, at close range — those combatants tend to be Alawites, the same minority sect that includes President Bashar al-Assad.

The Council’s statement is sure to be a factor in efforts by a former United Nations secretary general, Kofi Annan, to begin negotiating with the government on Monday on carrying out the six-point peace plan that he engineered as a special envoy.

But Mr. Assad has repeatedly shown himself to be impervious to international pressure. A string of international leaders have criticized Mr. Assad for making promises like respecting the cease-fire, and then continuing his attempt to put down the uprising by force. Indeed, there were reports of another case of Syrian shelling of civilians on Sunday, this time at Hama, a center of resistance where activists said dozens had been killed in new attacks. The details could not be confirmed.

Some Syrian opposition figures have criticized Western efforts to push the cease-fire when it was so clear that the government held it in contempt, and a few threatened vengeance against Alawites.

The issue also reverberated in partisan politics in the United States, with Mitt Romney, the presumed Republican presidential candidate, calling the massacre “horrific” and criticizing President Obama for backing the Annan plan.

“The Annan ‘peace’ plan — which President Obama still supports — has merely granted the Assad regime more time to execute its military onslaught,” the Romney statement said. “The United States should work with partners to organize and arm Syrian opposition groups so they can defend themselves.”

Russia has typically rejected any international effort to support the opposition in a way that might repeat the NATO military intervention in Libya, and despite strong statements, the West has avoided getting further embroiled in the Syria fighting out of fear of the long-term consequences.

On Sunday, the Council statement said that the “outrageous use of force” against civilians violated international law and commitments the Syrian government had made under the plan to stop using its heavy weapons in populated areas. It demanded that the Syrian government cease using heavy weapons immediately and pull its troops out of cities and towns. It also asked the United Nations observer mission in Syria to continue investigating the Houla attacks.

An earlier draft of the statement had more directly blamed the Syrian government for the massacre, but the Russians balked, saying they wanted to hear a closed briefing from the observers’ leader, Gen. Robert Mood, in Damascus. The Council statement emerged after that briefing.

Diplomats said the details General Mood presented closely followed those laid out by Ban Ki-moon, the United Nations secretary general, whose three-page letter demanded a concrete attempt to censure Syria and endorse the cease-fire.

In his letter, Mr. Ban skated very close to blaming Syrian government shelling for at least some of the deaths while carefully noting that the cause had not been completely determined. United Nations monitors “observed shotgun wounds and wounds consistent with artillery fire.”

The Russians seemed to be swayed by the arguments that it made little sense that the opposition, which is heavily Sunni Muslim, or even extremist jihadist elements, would kill so many of their own faith in cold blood, said one Security Council diplomat, speaking anonymously about a closed-door session.

“The patrol also saw artillery and tank shells, as well as fresh tank tracks,” Mr. Ban told the Council. “Many buildings had been destroyed by heavy artillery.”

The letter included other hints that government forces were involved, including the fact that up to eight bodies of civilians were removed from a government checkpoint in Teldo village. “The bodies bore signs of severe physical abuse,” the letter said.

Over all, the letter said the monitors found evidence of “appalling and brutal crimes, which involved indiscriminate and disproportionate use of force.”

One of the reasons that the Security Council had to act firmly, Mr. Ban said, is that ordinary Syrians are blaming the unarmed United Nations observers for not doing more to stop the violence, even if there are misconceptions about their role.

In Geneva, the top United Nations human rights official issued a statement saying that the “indiscriminate and possibly deliberate targeting of civilians” in Houla might amount to crimes against humanity or other international crimes. Navi Pillay, the United Nations high commissioner for human rights, called for Syrian cooperation with an independent, international investigation to determine what happened.

In Damascus earlier, the Syrian government rejected any tie to the massacre. “We unequivocally deny the responsibility of government forces for the massacre,” Jihad Makdissi, the spokesman for the Foreign Ministry, told a news conference. He reiterated government claims that the killings were the result of a terrorist attack, and he regretted that the United Nations and other foreign governments seemed to have accepted the opposition’s version of events.

Amateur videos said to be taken in the aftermath showed row after row of victims, many of them small children with what appeared to be bullet holes in their temples or what the opposition said were stab wounds.

Mr. Makdissi said the army did not send any tanks into the town of Houla, that security forces did not leave their positions and remained in a defensive posture. Instead, he said, hundreds of gunmen armed with machine guns, mortars and antitank missiles began attacking government positions in a skirmish that lasted much of the day and well into the night. Three soldiers were killed and 16 wounded, he said.

Yet he seemed to sidestep the main accusation made by the United Nations about shelling civilians. Mr. Makdissi did say that the Syrian government would not fire on its own civilians. Yet it has an established history of doing so throughout the uprising.

Mr. Makdissi said a judicial military committee inquiry had been formed that would investigate the killings and report back in three days.

Kuwait, which currently holds the presidency of the Arab League, announced an emergency meeting of Arab foreign ministers on the massacre. Syrian ties with the League were strained last year after its membership was suspended.

In Istanbul, Burhan Ghalioun, the president of the Syrian National Council, the main opposition group in exile, called on the international community to honor its commitment to protect Syrian civilians, saying if it did not, they would have no choice than to take matters into their own hands. “The international community suffers from a lack of will when it comes to protecting Syrian civilians,” Mr. Ghalioun, who is leaving the presidency, told a news conference. “The situation in Syria is truly explosive.”

His statement reflected the popular anger in Syria, especially among Sunni Muslims, that they were being targeted with impunity. Community chat rooms were filled with harsh, angry comments suggesting that the only solution to the crisis was to rid the country of the minority Alawite sect.

“Such massacres, such atrocities, definitely push the narrative of those who say this is a sectarian conflict,” said Fadi Salem, a program director at the Dubai School of Government. “The atmosphere is charged with sectarian feelings on both sides and this is a real threat.”