Syria’s 16-month bloodbath crossed an important symbolic threshold Sunday as the international Red Cross formally declared the conflict a civil war, a status with implications for potential war crimes prosecutions.

The Red Cross statement came as UN observers gathered new details on what happened in a village where dozens were reported killed in a regime assault. After a second visit to Tremseh on Sunday, the team said Syrian troops went door-to-door in the village, checking residents’ IDs and then killing some of them and taking others away.

According to the UN, the attack appeared targeted at army defectors and activists.

“Pools of blood and brain matter were observed in a number of homes,” a UN statement said.

On Sunday, Syria denied UN claims that government forces had used heavy weapons such as tanks, artillery and helicopters during the attack Thursday in Tremseh.

Syrian Foreign Ministry spokesman Jihad Makdissi said the violence was not a massacre — as activists and many foreign leaders have said — but a military operation targeting armed fighters who had taken control of the village.

“What happened wasn’t an attack on civilians,” Makdissi told reporters in Damascus. He said 37 gunmen and two civilians were killed — a far lower death toll than the one put forward by anti-regime activists, some of whom estimated the dead at more than 100.

“What has been said about the use of heavy weapons is baseless,” Makdissi added.

The United Nations has implicated President Bashar Assad’s forces in the assault. The head of the UN observer mission said Friday that monitors stationed near Tremseh saw the army using heavy weaponry and attack helicopters.

The fighting was some of the latest in the uprising against Assad, which activists say has killed more than 17,000 people. Violence continued across the country Sunday, with more clashes reported around the capital, Damascus.

The bloodshed appeared to be escalating. On Sunday, the International Committee of the Red Cross said it now considers the Syrian conflict a civil war, meaning international humanitarian law applies throughout the country.

Also known as the rules of war, humanitarian law grants all parties in a conflict the right to use appropriate force to achieve their aims. The Geneva-based group’s assessment is an important reference for determining how much and what type of force can be used, and it can form the basis for war crimes prosecutions, especially if civilians are attacked or detained enemies are abused or killed.

“We are now talking about a non-international armed conflict in the country,” ICRC spokesman Hicham Hassan said.

War crimes prosecutions would have been possible even without the Red Cross statement. But Sunday’s pronouncement adds weight to any prosecution argument that Syria is in a state of war — a prerequisite for a war crimes case.

Previously, the ICRC had restricted its assessment of the scope of the conflict to the hotspots of Idlib, Homs and Hama, but Hassan said the organization had determined the violence has widened

“Hostilities have spread to other areas of the country,” Hassan told The Associated Press. “International humanitarian law applies to all areas where hostilities are taking place.”

Although the armed uprising in Syria began more than a year ago, the ICRC has previously hesitated to call it a civil war — though others, including United Nations officials, have.

That is because the rules of war override and to some extent suspend the laws that apply in peacetime, including the universal right to life, right to free speech and right to peaceful assembly.

Stephen M. Saideman, professor at the Norman Paterson School of International Affairs in Ontario, Canada, doubted whether the Red Cross declaration would change anything significant on either side.

Assad and his supporters won’t stop fighting or change their tactics because they have too much to lose, Saideman said. The opposition “can have their spirits lifted by this, but they have been fighting a civil war for quite a while. So it is not clear how this announcement improves much their ability to recruit or to reduce divisions among the many rebel groups.”

On Saturday, UN observers entered Tremseh, a community of 6,000 to 10,000 people in a farming region along the Orontes River northwest of the city of Hama. They found pools of blood in homes along with spent bullets, mortars and artillery shells, adding details to the emerging picture of what anti-regime activists have called one of the deadliest events of the uprising.

Dozens of other bodies have already been buried in a mass grave or burned beyond recognition, and activists are still struggling to determine the total number of people killed.

Estimates of the dead ranged from 100 to 152. Activists expected those figures to rise since hundreds of residents remain unaccounted for, and locals believe bodies remained in nearby fields or were dumped into the Orontes River.

Some of the evidence suggested that, rather than the outright shelling of civilians depicted by the opposition, the violence in Tremseh may have been a lopsided fight between the army pursuing the opposition and activists and locals trying to defend the village. Nearly all of the dead are men, including dozens of armed rebels.

Independent verification of the events is nearly impossible in Syria, one of the Middle East’s strictest police states, which bars most media from working independently in the country.

The observers are in the country as part of a faltering peace plan by UN special envoy Kofi Annan, who has been trying for months to negotiate a solution to Syria’s crisis.

Although much of the international community has turned on Assad, Damascus still has some key allies — including Russia and Iran. The Kremlin announced Sunday that Annan will meet President Vladimir Putin on Tuesday.

Also Sunday, Iranian Foreign Minister Ali Akbar Salehi said Tehran is ready to invite Syrian opposition groups and government envoys for talks, the semiofficial ISNA news agency reported.

Any proposal from Iran is likely to be rebuffed by rebel groups, which have rejected negotiations with Assad’s government and have criticized Tehran for standing by its allies in Damascus. But the offer suggested Iran is seeking a more active role in mediation efforts after last week’s visit to Tehran by Annan, who is seeking to keep alive his flagging peace efforts.