The United States and 10 other countries expelled Syrian diplomats Tuesday after blaming government forces for last week’s massacre of more than 100 villagers in central Syria, but they again stopped short of calling for more aggressive action to end the violence.

Despite expressions of outrage and agreement that the situation in Syria has reached what U.N. special envoy Kofi Annan called a “tipping point,” the Obama administration and its major allies said they would continue to rely on diplomatic, political and economic pressure against Syrian President Bashar al-Assad.

U.N. monitors who visited the village of Houla, outside Homs, found that all but about 20 of 108 victims had been “summarily executed,” including “entire families . . . shot in their houses,” Rupert Colville, spokesman for the Office of the U.N. High Commissioner for Human Rights told reporters in Geneva. The rest, he said, were killed by artillery fire. Nearly half of the victims of Friday’s massacre were younger than 10.

Annan, who traveled to Damascus, the Syrian capital, in a bid to salvage a six-point U.N. peace plan, said he had appealed to Assad for “bold steps — not tomorrow, now — to create momentum for implementation of the plan.” Annan called for an immediate end to violence by the Syrian military and government-backed militias and urged armed rebels to stop attacks.

Others used sharper language to assign blame for one of the worst atrocities since the anti-
Assad Syrian uprising began 14 months ago.

“These were regime-sponsored thugs who went into villages, went into homes and killed children at point-blank range and their parents,” State Department spokeswoman Victoria Nuland said. She said the Syrian “thug force mirrors the same force that the Iranians used” to put down a nascent political uprising in 2009 and suggested that Assad was acting on Iran’s advice and assistance.

Herve Ladsous, the U.N. undersecretary general in charge of peacekeeping, said the government was responsible for those killed by shelling. The rest, he said, were shot or stabbed in an assault that “probably points the way to the shabiha.” The term refers to pro-government militias belonging to Assad’s Alawite sect; Houla residents said the shabiha had gone house to house on a killing rampage in the Sunni village Friday night.

Opposed to tougher action

As more details of the massacre emerged, 11 governments — including the United States and its major NATO allies — made coordinated announcements that they were expelling top Syrian diplomats. The Obama administration said it had given the Syrian charge d’affaires, Zuheir Jabbour, and several other senior diplomats 72 hours to leave the country, although the embassy in Washington would remain open with low-level staff.

But despite the harsh denunciations — Nuland called the killings “absolutely indefensible, vile, despicable,” and French Foreign Minister Laurent Fabius described Assad as “the murderer of his people”— arguments against international military intervention “are still the same,” said a senior European diplomat.

“We’re just not convinced that our intervening is going to make the conflict any nicer,” said the diplomat, speaking on the condition of anonymity about internal deliberations. “We are worried that we are going to unleash something that we will not be able to control.”

The international community is too divided to come up with effective ways of putting pressure on the Assad regime, said Salman Shaikh, director of the Brookings Doha Center. Russia, with veto power in the U.N. Security Council, remains opposed to tougher action against its chief Middle Eastern ally, as does China.

“This gruesome incident could give real momentum to diplomatic efforts, but, so far, it’s not had much effect,” Shaikh said. “There is still the hope among key Western powers that the Russians will come round. But I don’t think it’s really changing tack.”

But the Russians are only one part of the policy conundrum in Syria.

The Syrian opposition, despite Western efforts to help it organize, remains fractured. It is dominated by Sunnis, a fact that causes alarm among Syria’s powerful minority groups, and has no political consensus on what to do should Assad fall. Locally based opposition groups resent the ­exile-based political leaders who have won the backing of the United States and other powers, and there is little coordination between the armed rebels and the political groups.

Some regional powers, led by Saudi Arabia, see deposing Assad as a way to damage arch enemy Iran. The Saudis and others in the region are funding arms shipments to the rebels and have called for outside military intervention.

But Syria’s closest neighbors — Turkey, Jordan and Lebanon — fear the chaos and sectarian strife that could follow a Syrian collapse. Before any intervention, Turkey wants a strong legal framework, ideally with a U.N. resolution, and assurances of participation from Western powers.

Although NATO boasts of its successful Libya intervention, most of its members are opposed to similar action in Syria, with its far stronger military and air defenses. The Pentagon, while saying it has formulated potential options for President Obama, emphasized Tuesday that it has gotten no White House request for military plans.

The Russia factor

The Syrian dilemma has provided partisan political fodder at home. Presumptive Republican presidential nominee Mitt Romney on Tuesday criticized what he called Obama’s “lack of leadership” and “policy of paralysis.”

Romney said the administration should “increase pressure on Russia” to stop arming Syria and blocking stronger U.N. action and should start arming the Syrian opposition.

But among the allies, “the judgment now is that if you go down a road where you’re taking some fairly tough decisions in terms of your bilateral decisions with Russia,” there is a price to be paid, the European diplomat said. “We need Russia for other things,” including nuclear negotiations with Iran and North Korea.

Annan’s deputy, Jean-Marie Guehenno, is scheduled to brief the Security Council on Wednesday. Council diplomats said they expect to hear later in the week from Annan, whose U.N. mandate to arrange a cease-fire and negotiations over a new government has a month remaining.

“Our next U.N. step is to pursue a Chapter 7 resolution,” Nuland said.

Although such resolutions can be worded to endorse military intervention, the administration has made clear that it would utilize that step to expand economic and diplomatic sanctions on Syria.

A new council resolution would also require agreement from Russia and China.

Sly reported from Beirut. Staff writer Colum Lynch in New York contributed to this report.