DAMASCUS — 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 United Nations 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 small farming community, checking residents’ IDs, and then killing some and taking others away.
According to the UN, the attack appeared to target army defectors and activists.
Syria denied UN claims that government forces had used heavy weapons such as tanks, artillery, and helicopters during the attack Thursday.
Jihad Makdissi, Syria’s foreign ministry spokesman, said the violence was not a massacre — as activists and many foreign leaders have alleged — 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 Sunday in Damascus. He said 37 gunmen and two civilians were killed — a far lower death toll than the one put forward by antiregime activists, who estimated the dead at more than 100.
‘‘What has been said about the use of heavy weapons is baseless,’’ Makdissi said.
The UN 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 weapons and 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 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 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 noninternational armed conflict in the country,’’ said Hicham Hassan,a Red Cross committee spokesman.
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 Red Cross committee had restricted its assessment of the scope of the conflict to the hotspots of Idlib, Homs, and Hama. But Hassan said the organization concluded the violence was widening.
Although the armed uprising in Syria began more than a year ago, the committee had hesitated to call it a civil war — though others, including UN officials, have done so.
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.
When the Red Cross says something ‘‘it’s always very persuasive,’’ said Louise Doswald-Beck, a professor of international law at the Geneva Graduate Institute. In legal terms, that means a court would probably not decide differently.
But as an internal conflict officially becomes a civil war, the security environment shifts from regular law enforcement to a situation in which international law permits the government to attack rebel fighters, Doswald-Beck said.
Stephen M. Saideman, professor at the Norman Paterson School of International Affairs in Ontario, doubted if the Red Cross declaration would change anything significant.
Assad and his supporters will not 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.”
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 blood and remains in homes, along with spent bullets, mortar rounds, and artillery shells.
Dozens of bodies have already been buried in a mass grave or burned beyond recognition, and activists were struggling to determine the number of people killed. Estimates range from 100 to more than 150 dead. Hundreds of residents remain unaccounted for.
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 the dead are men, including dozens of armed rebels.
The Kremlin announced Sunday that Kofi Annan, the UN’s special envoy, will meet President Vladimir Putin on Tuesday.
Also Sunday, Iranian Foreign Minister Ali Akbar Salehi said his country is ready to invite Syrian opposition groups and government envoys for talks, the semiofficial ISNA news agency reported.