BEIRUT, Lebanon — Syria said Wednesday that rebels stormed a pro-government television station in a Damascus suburb, killing employees and blowing up the station in an audacious predawn assault, but rebels said the attackers were defectors from the elite Republican Guard, considered to be the most loyal core defenders of President Bashar al-Assad.


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.