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. The state-run news agency said at least 25 men had been killed. In the video, the narrator said the victims were members of the "shabiha," or pro-regime gunmen who have been accused of involvement in earlier massacres of Syrian civilians.
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 civil war.
The government has used heavy weapons and unleashed snipers and loyalist fighters, but rebels also 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 Friday that Iran -- one of Syria's most loyal allies -- should be part of the solution to the conflict.
An international meeting on Syria set for next Saturday is in disarray over the involvement of Iran. The United States has vehemently opposed the participation of Iran, which Russia is demanding.
In another development, Syria said it shot down a Turkish military plane that entered Syrian air space, and Turkey vowed to "determinedly take necessary steps" in response.
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 Friday night 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.
SANA said the bodies found in the rebel-held area of Daret Azzeh near Aleppo had been mutilated by terrorist groups. The government refers to rebels as terrorists.
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.
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.