The United Nations ratcheted up international pressure on the Syrian government Monday with the release of a report that documents the torture and killing of civilians by state security forces, in a step that could prompt action by the U.N. Security Council.

The authors of the report, who interviewed more than 200 people, concluded that Syrian military and security forces committed crimes against humanity in the eight-month-old crackdown on dissent.

The report, by the Independent International Commission on Syria, documents evidence that high-ranking officers across the country issued orders to shoot at civilian residences and unarmed protesters. It also re­cords evidence of systemic torture and the killing of hundreds of children.

The chairman of the commission, Paulo Pinheiro, expressed concern that many crimes committed by security forces were probably going unreported because the government has placed strict limitations on journalists.

“There are killings of children, sexual violence, especially against boys. . . . I think we have been able to demonstrate very scary patterns of human rights violations on a scale not always revealed by the international media,” Pinheiro said.

Nadim Houry, director of the Beirut office of Human Rights Watch, said the report could persuade some countries that have been supportive of Syrian President Bashar al-Assad to back measures against him and even encourage Syria to accept international monitors in the most violent areas of the country.

“What is driving the violence in Syria now is that the authorities still believe that there is a military option to crush the protesters,” Houry said. “It is pushing the country into a very dangerous vortex.” A plan to send monitors into the country, proposed by the 22-member Arab League, was rejected by Syria.

The U.N. report comes as international condemnation of the Assad government grows. On Sunday, the Arab League approved economic sanctions against Syria, and Europe and Turkey are set to tighten existing measures.

Susan E. Rice, the U.S. ambassador to the United Nations, said Monday evening: “The United States has long held the view . . . that it’s past time for the Security Council to take much more decisive action with respect to Syria.”

“We think it time to revisit the question of what might be possible in New York,” she added. “We certainly will be talking to partners in the council and outside the council about what appropriate next steps might be.”

Peter Wittig, the German ambassador to the United Nations, said the Arab League’s decision to sanction Syria should be followed by Security Council action.

“I think the [Security] Council cannot stand idly by” after the Arab League’s decision, he said. “The council should take up that decision and endorse and reinforce it.”

Syria has become increasingly isolated at the United Nations. Last week, several Arab countries co-sponsored a resolution in the U.N. General Assembly denouncing Syria’s human rights violations. Not a single Arab country supported Syria.

On Aug. 3, the Security Council adopted a statement condemning Syria’s violent crackdown on protesters, but China and Russia last month vetoed a European-drafted resolution that recommended possible measures against Syria.

The Arab League’s decision to suspend Syria’s membership in the organization raised expectations that the Security Council would take up the matter again. Given the growing Arab condemnation of Syria, Beijing and Moscow would be forced to pay a high political cost to block action in the council, particularly if a new resolution carried the backing of the Arab League.

But although Germany has called for Security Council action against Syria, other Western powers say they are not yet prepared for such a discussion. “We are building a case that is clearly heading to the Security Council,” said one Western diplomat, who spoke on the condition of anonymity because of the sensitivity of the situation. “But that doesn’t mean we are ready to push the start button.”

Syrian authorities have remained defiant. Foreign Minister Walid al-Moualem said at a news conference in Damascus on Monday, “The Arabs don’t want to admit the presence in Syria of groups of armed terrorists who are committing these crimes, abductions and attacks on public places.”

Peter Harling of the Brussels-based International Crisis Group was skeptical that the U.N. report would stem the bloodletting.

“The regime is facing huge international pressure,” Harling said. “The West has more or less unanimously turned against it, it has no support from the Arab countries or the Arab streets, and still it shows no sign of compromise. It has passed the point of compromise.”

Lynch reported from the United Nations.