BEIRUT, Lebanon — The leader of the Nusra Front, an affiliate of Al Qaeda in Syria, on Tuesday proposed an initiative aimed at halting the worst infighting yet between the armed opponents of President Bashar al-Assad since the start of the conflict nearly three years ago.

Deadly battles have raged in recent days across northern Syria between rebel forces and another Qaeda affiliate, known as the Islamic State of Iraq and Syria, or ISIS, that also wants to depose Mr. Assad’s government but aims to replace it with a monolithic Sunni extremist government that rules both countries.

Angered by what they call the tendency of the Islamic State of Iraq and Syria to commandeer resources, impose strict social codes, and kidnap and kill opponents, rebel groups have been attacking its bases and trying to drive out its fighters from towns and villages where they once held sway.

More than 270 people had been killed in four days of fighting as of Monday, according to the Syrian Observatory for Human Rights, an opposition group based in Britain with a network of contacts in Syria. The dead include 46 civilians, 129 rebel fighters and 99 fighters for the Islamic State of Iraq and Syria. Both sides have also executed prisoners, the Syrian Observatory said.

In an audio recording released online on Tuesday, the head of the Nusra Front, known as Abu Mohammed al-Jolani, said the infighting resulted from the “incorrect policies” of the Islamic State of Iraq and Syria. He called for a cease-fire and the establishment of an Islamic court to handle disputes, saying the violence could give Mr. Assad’s forces the opportunity to regain territory.

“The whole battlefield, including the foreign and local fighters, will pay the price of losing a great jihad because the regime will rebound when it was so close to vanishing,” he said.

While rebel forces have in the past established Islamic courts to administer individual towns and villages, the movement has never had a unified leadership that could impose discipline.

The authenticity of the Nusra Front leader’s statement could not be immediately confirmed.

The Syrian Observatory has reported that more than 130,000 people have been killed since the conflict began in March 2011. But the United Nations, which has been saying for months that the death toll has exceeded 100,000, announced on Tuesday that it had decided to stop updating its own tally, at least for the foreseeable future, because of the problems in verifying information.

“It was always very close to the edge in terms of how much we could guarantee the source material was accurate,” Rupert Colville, a spokesman for the United Nations high commissioner for human rights, told reporters in Geneva. He partly attributed the decision to the extremely limited ability of the United Nations to independently conduct fact-finding in Syria, making it “increasingly difficult for us to source and analyze the casualty figures in order to update them.”

Suspension of a United Nations update on casualties “will be a loss — we will now have only disparate sources of information,” said Hamit Dardagan, an author of a report on Syrian casualties by the Oxford Research Group, a London-based organization that put the toll at 113,700 as of November.

Mr. Dardagan, a founder of Iraq Body Count, a project begun in 2003 to record civilian casualties from the war in Iraq, also said the sectarian nature of the Syrian crisis would further complicate any data collection. “As any conflict intensifies and you have more refugee flows and more people displaced, that becomes more difficult,” he said in an interview.

The number of nongovernmental organizations able to work in Syria has been reduced by the increasing violence. Civilian groups that report events considered unfavorable to any of the warring parties have been targeted; most recently, Razan Zeitouneh, a rights activist who ran the Violations Documentation Center, and her colleagues were abducted from their office in a Damascus suburb. Parties on both sides also actively filter information they provide to the outside world to help their cause, and government restrictions and the threat of kidnapping and death have severely limited access for journalists.

United Nations agencies that do have some access have also described problems in verifying data. Officials with the World Food Program and the World Health Organization in Damascus said recently that because their officials could not reach many areas in Syria, they had set up local contacts to relay information to them, but that verification was difficult. Government ministries provide some data, but they are out of touch with branches in some rebel-held areas.

The United Nations reported some progress on Tuesday in the international effort to purge Syria’s chemical weapons stockpile. In a statement issued with the Organization for the Prohibition of Chemical Weapons, it said the first batch of the most dangerous materials in the stockpile had been exported from the country, loaded onto a Danish commercial vessel in the Syrian port of Latakia.

The statement said the Danish vessel would remain at sea until the second cargo of chemicals reached Latakia, when it would return to load them. The vessel was escorted by Danish and Norwegian naval vessels, the statement said, and China and Russia were providing further maritime security for the operation.

“This movement initiates the process of transfer of chemical materials from the Syrian Arab Republic to locations outside its territory for destruction,” said the statement by Sigrid Kaag, the United Nations official responsible for coordinating the effort.

The export and destruction of the most dangerous substances in the Syrian arsenal, which the statement called “priority chemical materials,” has long been considered the trickiest and most hazardous part of the operation, which Syria agreed to carry out as part of its pledge more than three months ago to renounce chemical weapons and join the treaty that bans them.

Under a Security Council resolution approved Sept. 27, all of Syria’s chemical weapons must be destroyed by the middle of 2014. The most dangerous chemicals were supposed to have been exported from the country by Dec. 31, but that stage of the operation was delayed because the war had made their overland transport to Latakia too dangerous to complete.

Source:The New York Times