BEIRUT (AP) - An online video showed more than a dozen bloodied corpses, some of them piled atop each other and in military uniforms, dumped beside a road in northern Syria in what the government Friday called a mass killing by rebel forces.
The circumstances of the deaths were not immediately clear, with the state-run news agency saying at least 25 men were killed. In the video - which The Associated Press could not independently verify - the narrator said the victims were members of the "shabiha," or pro-regime gunmen.
If confirmed, the video is yet another sign of the brutality of the Syrian conflict, which began in March 2011. As the fighting grinds on, Syria is descending into a civil war where gunmen prowl the streets and gruesome massacres are growing increasingly common.
The government has used heavy weapons and unleashed snipers and loyalist fighters, but rebels, too, have been accused of bloody attacks.
Civilians have been caught in the crossfire; activists estimate that more than 14,000 people have been killed since the start of the uprising against President Bashar Assad's regime.
In a desperate bid to end the violence after an earlier peace plan failed to do so, U.N. envoy Kofi Annan said that Iran - one of Syria's most loyal allies - should be part of the solution to the conflict.
Syria's state-run news agency, SANA, said the dead found in the rebel-held area of Daret Azzeh near Aleppo were killed and their bodies mutilated by terrorist groups. The government refers to rebels as terrorists.
The amateur video showing the corpses appeared to back up the allegation of a mass killing.
"The terrorist groups in Daret Azzeh committed a brutal massacre against the citizens, whom they had kidnapped earlier in the day," SANA said.
The report said at least 25 people were killed, but others were missing.
It was not clear whether the men were killed execution-style or died in clashes. An activist in the area, Mohammed Saeed, said rebels regularly collect the bodies of the dead from the government side and dump them by the side of the road so troops can collect them later.
The city of Aleppo, Syria's largest, has been relatively quiet, but towns and villages around it have seen intense clashes. Daret Azzeh has endured withering government shelling in the past two weeks as Assad's forces try to regain areas taken by rebels. The violence continued Friday, as Syrian troops shelled the area and used helicopter gunships in their attacks on rebels, Saeed said.
"The army has been trying to push through for days without success," Saeed said.
Government troops have been launching a major offensive on many areas throughout the country in the past two weeks to try to regain ground captured by the opposition. Attacks have mostly concentrated on Aleppo, the suburbs of the capital of Damascus, the central province of Homs, the southern region of Daraa and the eastern city of Deir el-Zour.
Activists reported that thousands of people demonstrated against the regime following Friday prayers in different parts of Syria, including Daraa, Aleppo, the northeastern region of Hassakeh and Damascus. The Britain-based Syrian Observatory for Human Rights said troops opened fire at protesters in Aleppo and the Damascus neighborhood of Mazzeh. Several casualties were reported.
The Syrian uprising began with regular anti-regime protests, although they have lost momentum as the revolt turned into an armed insurgency.
An international crisis meeting on Syria set for June 30 is in disarray over the involvement of Iran. The United States has vehemently opposed the participation of Iran, which Russia is demanding.
"I have made it quite clear that I believe Iran should be part of the solution," said Annan, the joint U.N.-Arab League envoy to Syria.
Annan told reporters in Geneva it was "time for countries of influence to raise the level of pressure on the parties on the ground." However, he had no specific proposals for changing his six-point peace plan, which he said Syria had not yet implemented but still might support.
"The longer we wait, the darker Syria's future becomes," said Annan, flanked by Maj. Gen. Robert Mood, the head of the struggling U.N. observer mission in Syria.
Western powers are clinging to the Annan plan, in part because there are no other clear options. There is little support for military intervention of the type that helped bring down Libya's Moammar Gadhafi during a 2011 uprising in that country, and several rounds of sanctions and other attempts to isolate Assad have done little to stop the bloodshed.
Mood praised the work of his 300 U.N. monitors, whose mandate ends next month. He conceded, however, that they are now largely confined to bureaucratic tasks and calling Syrians by phone because of dangers on the ground.
"Their commitment to the Syrian people has not faltered," he said. "Whether more observers or arming observers would be relevant to the situation on the ground, I'm far from convinced that that would help the situation on the ground."
The failure of Annan's peace plan has made it more difficult for outside observers, humanitarian workers and supplies to get in, or reliable information to filter out. Syria restricts the movement of journalists, making it hard to confirm accounts from either side.
Also Friday, the Observatory said four senior army officers have defected from the regime. The group provided a video purporting to show two brigadier generals and two colonels who declared they were joining the opposition.
The group said the defections came Thursday - the same day a Syrian fighter pilot flew his MiG-21 warplane to neighboring Jordan, where he was given asylum.
Thousands of soldiers have abandoned the regime, but most are low-level conscripts. The Free Syria Army, the loosely linked group of rebel forces, is made up largely of defectors.
Also Friday, Syria said Friday it shot down a Turkish military plane that entered Syrian air space, and Turkey vowed to "determinedly take necessary steps" in response.
It was the most clear and dramatic escalation in tensions between the two countries, which used to be allies before the Syrian revolt began in March 2011. Turkey has become one of the strongest critics of the Syrian regime's response to the uprising.
Syria's state-run news agency, SANA, said the military spotted an "unidentified aerial target" that was flying at a low altitude and at a high speed.
"The Syrian anti-air defenses counteracted with anti-aircraft artillery, hitting it directly," SANA said. "The target turned out to be a Turkish military plane that entered Syrian airspace and was dealt with according to laws observed in such cases."
Turkey issued a statement following a two-hour security meeting led by Turkish Prime Minister Recep Tayyip Erdogan, saying Syrian forces downed the plane and that the two Turkish pilots remain missing.
It said Turkey "will determinedly take necessary steps" in response, without saying what those actions would be.
AP writers Elizabeth A. Kennedy in Beirut, Selcan Hacaoglu in Ankarak, Turkey, and John Heilprin in Geneva contributed to this report.