The attack coincided with a new United Nations report on human rights violations in Syria that mostly castigated the Syrian government.

Rebels disputed the official account of the attack, saying the killers were defectors from Syria's elite Republican Guard, considered the most loyal core of defenders of Mr. Assad's inner circle. If the rebel version is confirmed, the attack would constitute a significant breach of security for those close to Mr. Assad, who said on Tuesday that Syria was now in "a state of war."

The attackers struck against the backdrop of increasingly bold rebel assaults in the Damascus area and an accelerated pace of high-level defections from Mr. Assad's military. Mr. Assad is also dealing with hostility from Turkey over Syria's downing of a Turkish military jet last week.

In a new twist possibly aimed at appeasing the Turks, Syria's information minister, Omran al-Zoubi, was quoted as telling a private Turkish broadcaster on Wednesday that Syrian antiaircraft gunners might have mistaken the Turkish plane for an Israeli one. "Turkish planes and Israel planes look like each other," he was quoted as saying by the broadcaster, A Haber.

In the struggle to find a diplomatic solution to Syria's turmoil, Kofi Annan, the special envoy to Syria for the United Nations and the Arab League, said he would convene a ministerial-level meeting on Saturday in Geneva involving what he has called countries of influence in the conflict. Mr. Annan's peace plan has been paralyzed since he announced it more than two months ago,

Participants in the meeting would include the five permanent members of the Security Council — China, France, Russia, Britain and the United States — and emissaries from the European Union, the Arab League and Turkey. But the list of invitees conspicuously omitted Iran, Syria's most important regional ally, which Mr. Annan had wanted to include. The United States and its allies objected strongly to Iran's participation, contending that Iran aids the Syrian leader's harsh repression of the 16-month-old uprising against him.

The conflicting accounts of who assaulted the television station, Al Ikhbaria, a satellite broadcaster, reflected the difficulties that outsiders face in determining the true course of events in the Syrian conflict, from which independent reporters and most international relief and monitoring officials are effectively barred.

Those difficulties were illustrated Wednesday in findings by a panel from the United Nations Human Rights Council in Geneva, which is investigating rights violations in Syria but has been blocked from conducting the inquiry inside Syria and has relied heavily on testimony from refugees and defectors. The panel said that it was unable to determine conclusively who was responsible for the May 25 massacre of 108 civilians in Houla, a string of villages in western Syria, but that it "considers that forces loyal to the government may have been responsible for many of the deaths."

While the investigators accused government forces of committing violations on "an alarming scale" in recent months, they also found that both sides had carried out summary executions. And they said the conflict had escalated significantly despite Mr. Annan's peace entreaties.

 "The situation on the ground has dramatically changed in the last three months as the hostilities by antigovernment armed groups each day take on more clearly the contours of an insurrection," the investigators said. "As a result of the estimated flow of new weapons and ammunitions, both to the government forces and to the antigovernment armed groups, the situation risks becoming more aggravated in the coming months."

The attack on Al Ikhbaria began before dawn, when assailants "planted explosive devices in the headquarters of Al Ikhbaria following their ransacking and destroying of the satellite channel studios, including the newsroom studio," which was destroyed, the official Syrian news agency, SANA, reported.

The news agency referred to the assailants as terrorists, the usual official description of Mr. Assad's armed opponents.

Al Ikhbaria, which means Syrian Satellite News, is privately owned but strongly supportive of the government. It is in the town of Drousha, about 14 miles south of Damascus.

Col. Malik Kurdi, a spokesman in Turkey for a rebel commander, Riad al-Assad of the Free Syrian Army, said the attack was carried out by a group of Republican Guard members who had decided to defect and had attacked other loyalist guards at the station. There was no way to independently verify the claim from Colonel Kurdi, who was interviewed by telephone from a refugee camp in southern Turkey.

The contradictory versions of events flowed partly from the information war between Mr. Assad's government and its adversaries.

Anti-Assad activists have proved adept at offering their narrative of the uprising through video clips showing the fighting between government and opposition forces and the bloody aftermath. In recent months, Syrian state media outlets have sought to use similar imagery — sometimes identical — to bolster accusations against the rebels.

On its Web site, SANA showed photographs of what it said were wrecked studios at Al Ikhbaria and quoted Mr. Zoubi, the Syrian information minister, as saying the attackers had perpetrated "the worst massacre against journalism and the freedom of media when they executed the Syria media figures in cold blood." Mr. Zoubi said the attackers had tied their victims' hands behind their backs before killing them.

In its report to the Human Rights Council on Wednesday, the United Nations panel said violations "are occurring across the country on an alarming scale during military operations against locations believed to be hosting defectors and/or those perceived as affiliated with antigovernment armed groups."

Paulo Pinheiro, the Brazilian chairman of the panel, said, "Gross human rights violations are occurring regularly in the context of increasingly militarized fighting."

Syria's ambassador to the United Nations in Geneva, Faysal Khabbaz Hamoui, said the panel had "fallen into the trap of prejudice" and threatened to withdraw Syria's cooperation from United Nations human rights bodies. He then walked out of the council chamber.

The panel warned that killings were increasingly driven by sectarian motives. "Where previously victims were targeted on the basis of their being pro- or antigovernment," it said, the investigators had "recorded a growing number of incidents where victims appear to have been targeted because of their religious affiliation."

Rod Nordland reported from Beirut, and Alan Cowell from London. Reporting was contributed by Hwaida Saad and Dalal Mawad from Beirut; an employee of The New York Times from Damascus, Syria; Nick Cumming-Bruce from Geneva; Sebnem Arsu from Istanbul; and Rick Gladstone from New York.