UNITED NATIONS — Special emissary Kofi Annan told the U.N. Security Council on Tuesday in a closed-door session that an expanding U.N. monitoring mission still stands a chance of calming the violence in Syria, despite reports of a spike in killings, including an alleged government attack on civilians in the town of Hama shortly after U.N. observers had visited the town.

But the U.N. peacekeeping chief, Herve Ladsous, told the council that Syria was balking at the observers being dispatched to the war-torn country, according to U.S. ambassador Susan Rice. Ladsous said that one U.N. observer had been rejected on the basis of nationality, and the government in Damascus had refused to to accept nationals from countries represented in the Friends of Syria, she said. That group, which has supported the Syrian opposition, includes the United States, Britain, France, Saudia Arabia, Turkey and Qatar.

Ladsous told the council that position was “unacceptable,” according to Rice. She spoke in her capacity as president of the Security Council.

Annan, a former U.N. secretary general who is serving as the U.N.-Arab League envoy for Syria, delivered a carefully worded briefing to the council that raised concern about the Syrian government’s reported attacks on Monday but urged continued support for his fragile diplomatic bid.

“Our patience has been tested severely — close to its limits,” he said, according to the briefing notes provided by a council diplomat. “But we have also seen signs that there is the possibility for the parties to implement a cessation of violence, which can lead to a political process and peaceful way out of the crisis.”

Annan said that he intends to press ahead with his efforts to start political talks between the government and the fragmented political, civil and military opposition groups. He said he would approach the Syrian government at the “appropriate time” and request President Bashar Al Assad appoint a representative to the talks. At the same time, he said, his team is pressing the opposition to develop a “more inclusive and representative” approach to political talks.

Annan said that while it is difficult for a handful of U.N. monitors to “assess the level of violence” throughout Syria, the scale of killing had “as a whole” had decreased since a U.N.-brokered cease-fire took effect on April 12. However, the violence spiked on Monday, he said, citing an upsurge of killing in Hama, where government forces reportedly attacked civilians in a suburb following a visit by U.N. monitors.

“I am concerned by media reports that, before and after [UN] observer visits, government troops have been active in civilian areas and launched attacks,” he said. “I am particularly alarmed by reports that government troops entered Hama yesterday after observers departed, firing automatic weapons and killing a significant number of people.”

Annan’s report came as the U.N. Security Council is straining to maintain unity despite widely divergent approaches by the council’s key powers. The United States and its European and Arab allies have been clamoring for a tougher approach to Syria, arguing that sanctions are required to prod the government to meet its obligations.

Russia and China, meanwhile, have preferred an exclusively diplomatic strategy, with pressure on both sides to pursue political talks.

Annan held out the hope that a beefed-up U.N. monitoring mission, which may expand to 300 unarmed observers in the coming weeks, could restore calm, citing the reduction of violence in the town of Homs following the arrival of U.N. observers. “There is a chance to expand and consolidate the cessation of violence,” he said. “Observers not only see what is going on, but their presence has the potential to change the political dynamics.”

Ladsous said there will be 30 U.N. monitors in Syria by April 30 and 100 more will arrive within a month, Rice said.

Annan concluded that Syria’s compliance with its commitments under his peace plan – known as the six-point plan — has been “partial” at best, noting that the “gestures” the government has taken so far “do not yet amount to the full and clear signal” of its commitment to embrace political change. But he also seemed to concede that any political settlement he is likely to deliver will involve moral compromises.

“Under the circumstances, the peace we are trying to build could never be perfect – and we have all been shocked by events in Syria. But if we succeed, the prospects are far better than any promised through war,” he said.

Annan said that he had received written assurances Saturday from Syrian Foreign Minister Wallid Moallem that “the withdrawal of massed troops and heavy weapons from in and around population centers is now complete and military operations have ceased.” Annan said he was “encouraged” by Moallem’s pledge but that “it should be understood that the only promises that count are the promises that are kept.”