BEIRUT (AP) -- Syrian state-run TV reported Friday that the leader of a powerful al-Qaida-linked rebel group has been killed _ a claim that if confirmed would be a huge blow to fighters trying to topple President Bashar Assad. At least one rebel commander denied the report.

Questions remained over whether Abu Mohammad al-Golani, head of  Jabhat al-Nusra, or the Nusra Front, had indeed died. State TV said he was killed in the coastal province of Latakia, but did not say when or give details. Later Friday, it removed the report from its website without explanation.

The Britain-based Syrian Observatory for Human Rights, which closely monitors the fighting in Syria, said senior Nusra Front leaders contacted by activists in Latakia and the eastern Deir el-Zour province denied al-Golani had been killed.

Other Nusra Front sources said they could not confirm or deny the report "because contact with al-Golani was cut," the Observatory said in a statement. A rebel commander in a Damascus suburb contacted by The Associated Press said he believed al-Golani was "alive and well" based on his contacts with other fighters including those from Nusra Front. He declined to elaborate or be identified for security concerns.

The report comes as the fragmented rebels have suffered significant losses on the battlefield.

Syrian troops killed at least 40 opposition fighters, including Nusra Front members, earlier Friday in an ambush near Damascus, the government said.

Assad's forces backed by Lebanese Hezbollah gunmen also seized control of a rebel ammunition supply route on a highway linking the capital to its eastern suburbs _ part of a blistering government offensive to bolster its position amid an international push for peace talks.

The Nusra Front has emerged as one of the most effective among rebel groups fighting Assad, and it has claimed responsibility for numerous suicide bombings against government targets. The U.S. State Department put the group on its list of terrorist organizations for its connections to al-Qaida.

Al-Golani, who fought previously in Iraq, is a shadowy figure who is believed to have spent time recently in rebellious suburbs south of Damascus. Rebels have also gained footholds in mountainous regions of Latakia, which is largely loyal to Assad, and he may have gone there to direct fighting.

Al-Golani gained prominence in April when he rejected an attempted takeover of the group by Abu Bakr al-Baghdadi, the head of the Islamic State of Iraq, revealing a growing rift within al-Qaida's global network.

Al-Golani at the time distanced himself from claims that the two groups had merged into a group called the Islamic State of Iraq and the Levant. Instead, he pledged allegiance directly to al-Qaida's leader Ayman al-Zawahri.

He said that al-Baghdadi's announcement of the merger was premature and that his group will continue to use Jabhat al-Nusra as its name.

The group is more popular in Syria than the ISIL, which is largely made up of foreign fighters and has been criticized for its brutality and for trying to impose a strict version of Islamic law in areas under its control.

Al-Golani's death would likely strengthen ISIL at a time of growing infighting between al-Qaida extremists and the more moderate rebels from the mainstream Free Syrian Army.

Assad's forces have been gaining ground in rebel-held areas around the capital, the seat of his power, and have made progress against outgunned and fragmented fighters in several areas.

On Friday, the state-run news agency SANA said 40 rebels died in the ambush near Otaiba, adding that soldiers seized a large arms cache, including anti-tank rockets.

The area is part of a region known as Eastern Ghouta, which was the scene of a chemical weapons attack in August believed to have killed hundreds.

The state-run Al-Ikhbariya television station broadcast footage showing more than a dozen bodies near the largely dried-out Otaiba lake, some wearing flak jackets strapped with ammunition. Automatic rifles and hand grenades lay nearby.

An unidentified Syrian army officer in the area told Al-Ikhbariya that foreign fighters were among the dead and that the ambush followed an intelligence tip.

The Observatory said at least 24 fighters, some of them foreign, were killed in the ambush, but it gave no further details and the differing death tolls could not be immediately reconciled.

The offensive coincided with an international push for a peace conference to be held in Geneva. Both sides want to bolster their position on the ground ahead of the talks, expected next month. No final date has been set, however, and it is unclear whether the sides will reach an agreement on the agenda.

The Supreme Military Council, which brings together a collection of loosely-knit rebel brigades under the emblem of the Free Syrian Army, said Friday it refused to sit down with Syrian officials involved in killing Syrians. Comments carried by the Syrian National Coalition, the group's political wing, also dismissed the proposed talks for lacking a way to reach concrete results.

In other violence, a car bomb blew up near a mosque in in the village of Wadi Barada outside of Damascus shortly before Friday prayers ended. The Observatory said 40 people were killed in the blast and dozens wounded. SANA said the car blew up as it was being rigging with explosives. The agency said a number of people were killed.

The ambush near Damascus came hours after Assad's forces captured the town of Hatitat al-Turkomen south of the city, securing a key highway that links the capital with the Damascus International Airport.

North of Damascus, rebels and government forces clashed for a fifth consecutive day in the Christian town of Sadad. Al-Qaida-linked groups captured a checkpoint earlier this week that gave them control of the western part of the town.

Archbishop Silwanos Al-Nemeh told The Associated Press in a telephone interview as many as 3,000 civilians were trapped, and he appealed for international organizations to help civilians flee the area.

Also Friday, Norway rejected a U.S. request for it to receive the bulk of Syria's chemical weapons for destruction, saying it doesn't have the capabilities to complete the task by the deadlines set by an international chemical watchdog.

The United Nations has set a mid-2014 deadline for the destruction of Syria's arsenal _ a deadline Brende said was too tight for Norway.

On Friday, the OPCW said its inspectors visited a site the day before and verified that all of its previous chemical weapons-related equipment has been dismantled. That brings to 19 the total number of sites visited by OPCW inspectors, of 23 that have been disclosed by Syria.

The Syrian conflict has left more than 100,000 people dead and driven nearly 7 million more from their homes.