Agreement on additional international action in Syria appeared more remote than ever following a massive suicide bombing on Thursday in Damascus, as foreign leaders pointed fingers of responsibility for the violence in opposite directions.

Obama administration officials said they could not confirm who carried out the attack, but placed the blame squarely on Syrian President Bashar al-Assad for allowing the situation to escalate rather than complying with a United Nations resolution ordering a cease-fire supervised by U.N. monitors.

Russia, whose approval is necessary at the Security Council for any further U.N.-authorized action, accused countries supporting the U.S.-backed Syrian opposition of intentionally instigating heightened violence to justify military intervention.

“Some of our foreign partners are taking steps to ensure, both literally and figuratively, that the situation explodes,” Russian Foreign Minister Sergei Lavrov said, making clear that he was “referring to the bombings.”

Lavrov made his remarks at a news conference in Beijing, alongside his Chinese counterpart, Foreign Minister Yang Jiechi, who reiterated his government’s rejection of “outside military intervention in Syria.”

The deadliest bombing in the Syrian capital since the uprising began 16 months ago came as the U.N. monitoring mission was widely seen as failing. The United States and its allies, senior administration officials said, are discussing the criteria for declaring it dead and what to do afterward.

U.S. officials spoke on the condition of anonymity and would not allow quotations to be used on the sensitive issue.

Russia and China, which vetoed previous Syria resolutions, agreed to the mission headed by former U.N. secretary general Kofi Annan. Its terms included deployment of 300 unarmed U.N. monitors to observe compliance with a promised Syrian military withdrawal from towns and cities and an overall cease-fire — neither of which has been achieved. About 100 monitors have arrived in Syria, with the remainder due by the end of the month.

“Assad’s calculation is that he can try to use the Annan mission to continue to be a cover for his ability to do what he’s doing,” said Senate Foreign Relations Committee Chairman John F. Kerry (D-Mass.), who just returned from a trip to the region.

“I think it’s not going to work,” he said of the U.N. effort, but Annan should “have the right to decide when and if it won’t. We shouldn’t be pre-declaring in any fashion. “

For the moment, an administration official said, U.S. strategy is to allow the mission to play itself out unless events — such as attacks against the monitors themselves — make that impossible.

Defense Secretary Leon E. Panetta reiterated Thursday that the Pentagon continues “to make all kinds of plans with regards to possible approaches in Syria. And if the president of the United States asks us to respond in particular ways,” Panetta said at a news briefing, “we’re prepared to do that.”

Those contingency plans include military protection of corridors for humanitarian assistance to Syrian civilians or of a “safe zone” where the opposition could organize, as well as an air assault on Syria. But administration officials said they are not considering pursuing any of these military options.

Future steps, officials said, are likely to include more of the same — increasing sanctions and diplomatic isolation of Assad and his government, much of which would also require approval from Russia and China.

“There are people who want to put pressure on us to change our position,” Lavrov said. “But we will not succumb to this pressure.”

Bombings like the Damascus suicide attack, which the Syrian government blamed on terrorists, “bolster the Russian case” against aiding the opposition, said Shashank Joshi of the Royal United Services Institute, a British think tank.

But suspicions that the bombings were carried out by jihadists who have infiltrated the opposition, he said, “also bolster the internal American case that this conflict is simply too complicated and too inflammable to actually put U.S. forces at risk in any meaningful way.”

The most likely partners in any U.S. military operation, including those who took part in last year’s Libya intervention, are even more reluctant. “This time last year, Joshi said, the British government “was in a much stronger position” both politically and economically. “We just entered a double-dip recession last week.”

France, in the midst of installing a new government whose policies have not been fully articulated, sees the two situations as vastly different.

“It’s not a small difference with Libya, it’s a huge difference,” one French official said. “The opposition has no territory” in Syria, and little unity. Syria’s air defenses dwarf those of Libya’s, and its vast stores of chemical and biological weapons, currently under Assad’s control, could be up for grabs if the government falls.

“But it’s also a political question,” the French official said. “For many, particularly the Europeans, the only legitimate body to call for military action is the United Nations.”

On Syria’s borders, Turkey and Jordan have said that no military action is possible without U.N. approval; both fear being left to pick up the pieces if the Syrian government disintegrates without an internationally sanctioned and guided replacement.

Wealthy Persian Gulf states have given money and rhetorical support, but are awaiting U.S. leadership before taking further steps.

Staff writer Colum Lynch at the United Nations contributed to this report.