If the rebel claim is confirmed, the attack would constitute a significant breach of security for the inner circle of Mr. Assad, who said on Tuesday that Syria was now in a state of war — a markedly different description of a conflict he had previously characterized as a crime wave by foreign-backed terrorists. The attack on the television station also came against the backdrop of increasingly bold and organized rebel assaults in the Damascus area and an increased pace of high-level military defections.

It also came as Kofi Annan, the special envoy to Syria from the United Nations and the Arab League whose peace plan has been paralyzed since he announced it more than two months ago, said he would convene a ministerial-level meeting on Saturday in Geneva representing what he has called countries of influence in the conflict, including the five permanent members of the Security Council and representatives from 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 had expressed strong objections to Iran's participation, contending that it had aided and abetted the Syrian leader's harsh repression in the 16-month-old conflict.

Mr. Annan said in a statement that the group's objectives would be to find ways to implement his peace plan and "agree on guidelines and principles for a Syrian-led political transition that meets the legitimate aspirations of the Syrian people."

The conflicting accounts of who carried out the assault on the television station, the al-Ikhbaria satellite broadcaster, reflected the difficulties that outsiders face in ascertaining 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. The panel said it was unable to determine conclusively who was responsible for the May 25 massacre of 108 civilians in the western region of Houla, but "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 determined that the nature of the conflict had changed, escalating 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 entirely destroyed," the official Syrian news agency, SANA, reported.

The news agency referred to the assailants as terrorists — the usual official language to denote armed opponents of Mr. Assad's government. While initial reports from SANA said three employees were killed, a subsequent official estimate put the death toll at seven.

The station, privately owned but strongly supportive of the government, is in the town of Drousha, around 14 miles south of Damascus.

The Associated Press quoted one of its photographers who visited the compound as saying that five portable buildings used for offices and studios had collapsed, with blood on the floor and wooden partitions still on fire. Some walls had bullet holes, the photographer said.

Hours later, The A.P. said, the station was able to broadcast a rally in Damascus's main square against the attack on its premises.

Col. Malik Kurdi, a spokesman in Turkey for a rebel commander, Riad al-Assad of the Free Syrian Army, said the attack was the result of the defection of a group of Republican Guards who had decided to change sides and attacked other guards at the station who had remained loyal.

If confirmed, his assertion would be another sign of unraveling control in Damascus, where violence has increased markedly, including an attack on the Republican Guard base near the presidential palace on Monday. There was no way to independently verify Colonel Kurdi's claim.

He 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.

The government's opponents have proven 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 the government's accusations against the rebels.

On its Web site, SANA showed photographs of what it said were wrecked studios at al-Ikhbaria and quoted the Syrian information minister, Omran al-Zoubi, as saying the attackers perpetrated "the worst massacre against journalism and the freedom of media when they executed the Syria media figures in cold blood."

The mounting violence offered a telling backdrop to remarks on Tuesday by Mr. Assad to his cabinet, reported by SANA, in which he said, "We live in a state of war."

As such, he said, "all our policies, directives and all sectors will be directed in order to gain victory in this war."

In its report to the Human Rights Council on Wednesday, the United Nations investigators' panel said, "Human rights 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, Faisal Khabbaz Hamoui, said the panel had "fallen into the trap of prejudice" and warned that Syria would withdraw its 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 as opposed to political 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."

The panel was appointed last year and was giving its third update on developments in Syria. It said it had received reports of summary executions by government forces, sometimes targeting named individuals and family members linked to the opposition, as well as large-scale executions of scores of people living in areas under attack by government forces.

The commission said it had also received many reports of summary executions by antigovernment rebels, foreign fighters and people suspected of being informers or collaborators.

A Free Syrian Army soldier told the panel that captured soldiers from the Alawite sect, from which Mr. Assad draws strong support, are usually executed immediately, while soldiers from other sects are given the option of joining the opposition.

The commission drew attention to the plight of children caught in the conflict and the use of sexual violence against men, women and children, particularly by pro-government forces. It cited reports that boys over the age of 14 had been targeted as members of antigovernment groups in areas where Assad loyalists hold sway and that children as young as 10 had reported being tortured during interrogation by security forces to admit that older relatives supported resistance to the government. It expressed particular concern that opposition forces were using children as medical porters and messengers, "exposing them to risk of death and injury."

The commission found that crimes of sexual violence occurred mainly when government forces entered villages and urban neighborhoods searching for rebels or during interrogation in detention. Fear of rape and sexual assault is discouraging girls from attending schools in some areas, the commission reported, also noting, "Many of the women interviewed who had sought refuge in neighboring countries had done so because they feared sexual assault."

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