Syrian army defectors killed at least 27 government forces in clashes yesterday in the southern province of Daraa, activists said.
It was one of the deadliest rash of attacks by rebel troops since the uprising against President Bashar Al Assad's regime began nine months ago.
Citing witnesses on the ground, the Britain-based Syrian Observatory for Human Rights said three separate clashes erupted at dawn in Daraa, where the uprising began in March. The allegations could not be independently confirmed.
The claims of intensifying fighting between government forces and insurgents came two days before Arab League foreign ministers convene in an emergency meeting in Cairo to respond to a proposal by Syria to admit observers in exchange for an end to regional sanctions.
The 22-member regional bloc last month suspended Syria's membership in the group to protest its government's crackdown on pro-reform demonstrators.
As evidence of deep fissures in Mr Al Assad's military mounted, he faced renewed demands to step down from power.
During a visit to Libya yesterday, the French foreign minister, Alain Juppe, accused Mr Al Assad's government of committing crimes against humanity on a daily basis.
"More than 5,000 killed, three million Syrians are affected by bloody repression, unspeakable abuse and daily crimes against humanity," Mr Juppe told university students during a visit to Libya's capital Tripoli. "How many more victims does the world still need before it understands that Bashar Al Assad must go?"
Less than a day earlier, the US predicted Mr Assad's downfall, saying the repression by his government may allow him to hang on to power, but only for a short time.
"Our view is that this regime is the equivalent of dead man walking," Frederic Hof said in particularly scathing remarks to members of US Congress on Wednesday.
Mr Hof, the state department's point man on Syria, said Syria was turning into "Pyongyang in the Levant", a reference to the North Korean capital. He said it was difficult to say how much time Mr Al Assad has left in power but added: "I do not see this regime surviving."
In an apparent bid to promote defections, Mr Hof warned Syrian troops and Mr Al Assad's top aides that their president may be setting them up for possible war crimes or criminal charges by claiming in an interview last week that the army was not his to command.
"It's difficult to imagine a more craven disclaimer of responsibility," Mr Hof said. "Perhaps it is a rehearsal for the time when accountability will come."
The prospect of eventual war-crimes charges being lodged against top members of Mr Assad's government loomed larger yesterday.
Human Rights Watch issued a report alleging that dozens of Syrian military commanders and officials authorised or gave direct orders for widespread killings, torture and illegal arrests during the wave of anti-government protests.
The 88-page report by the New York-based group is based on more than 60 interviews with defectors from the Syrian military and intelligence agencies. It identifies 74 commanders and officials behind the alleged abuse.
"Defectors gave us names, ranks, and positions of those who gave the orders to shoot and kill, and each and every official named in this report, up to the very highest levels of the Syrian government, should answer for their crimes against the Syrian people," said Anna Neistat, the associate director for emergencies at Human Rights Watch.
All of the defectors interviewed said their commanders gave standing orders to stop the overwhelmingly peaceful protests throughout the country "by all means necessary". They understood the phrase as an authorisation to use lethal force, especially because they had been given live ammunition instead of other means of crowd control.
About half the defectors interviewed by the human rights organisation said the commanders of their units or other officers also gave them direct orders to fire at protesters or bystanders and reassured them that they would not be held accountable.
The report quotes defectors as saying that in some cases, officers themselves participated in killings. It said the abuses constitute crimes against humanity and that the UN Security Council should refer Syria to the International Criminal Court.
Mr Assad's regime claims armed gangs and terrorists are behind the uprising, not protesters seeking more freedoms and reform in one of the most authoritarian regimes in the Middle East.
Iraq will send a delegation to Syria to try to convince Damascus to implement a Baghdad peace deal, the Iraqi prime minister, Nouri Al Maliki, said yesterday. The initiative is aimed at opening a dialogue between the opposition and the Syrian government to reach a result that satisfies both sides, he said.
The government has sealed off the country to most outsiders while alleging that the uprising is the work of foreign extremists, not true reform-seekers aiming to open the tightly controlled political system.
The United Nations and other observers dismiss that notion entirely, blaming the regime for widespread killings, rape and torture.
"Try as he may to distance himself from responsibility for his government's relentless brutality, President Assad's claim that he did not actually order the crackdown does not absolve him of criminal responsibility," said Ms Neistat of Human Rights Watch. "As the commander in chief of the armed forces, he must have known about the abuses - if not from his subordinates, then from UN reports and the reports Human Rights Watch sent him."
* With reporting from The Associated Press and Agence France-Presse