Foreign extremists are escalating the conflict in Syria by joining the fighting in growing numbers, the UN commission investigating human rights abuses in the country warned Monday, DPA reported.
"Such elements tend to push anti-government fighters towards more radical positions," the panel's chairman, Paulo Pinheiro, said at the United Nations Human Rights Council in Geneva.
Pinheiro, who was speaking during the 21st session of the UN's Human Rights Council, did not specify where the foreign fighters were coming from. He said that some were fighting alongside the rebels, while others were operating independently.
"The commission confirmed the increasing presence of foreign elements, including jihadist militants, in Syria," he reported.
He added that sectarian violence between Sunni Muslims on one side, and Shiites and Alawites on the other, was also on the rise.
But the regime of Syrian President Bashar al-Assad has also been receiving foreign help. Iran's Revolutionary Guards, for instance, acknowledged providing such assistance for the first time.
Pinheiro stressed that government forces and allied militias had committed more serious war crimes and human rights violations than the rebels.
He highlighted daily indiscriminate attacks on civilians, as well as reports that, in several areas, trapped civilians are "barely managing to survive."
The investigation commission said its report should be sent to the UN Security Council, as it is the only body that can tell the International Criminal Court in The Hague to take up the matter.
Nadim Houry, deputy Middle East director at New York-based Human Rights Watch, said in a statement that the UN Security Council should refer the situation in Syria to the ICC.
"An ICC referral would give the ICC jurisdiction to investigate crimes committed by both the government and the opposition,"the statement said.
"Extrajudicial or summary executions of detainees in the context of an armed conflict are war crimes, and may constitute crimes against humanity if they are widespread and systematic," it added.
The top commander of Iran's powerful Revolutionary Guard admitted for the first time that members of his force are in Lebanon and Syria, offering what he described as "intellectual and advisory help," according to Arab media reports.
But Major General Mohammed Ali Jaffari denied that the guards were taking part in the fighting, according to Iranian news agency ISNA.
His comment nevertheless appeared to confirm accusations by rebels that Iran is helping al-Assad's regime.
Lebanese President Michel Suleiman demanded Iranian ambassador to Lebanon, Ghazanfar Rokn-Abadi, provide an official clarification.
In August, rebels captured what they said were some 20 Iranians and posted a video of them with their Revolutionary Guards identification documents. The rebels have also accused Iran's Lebanese allies, Hezbollah, of helping the regime.
Tehran and Hezbollah both denied such charges at the time.
Inside Syria, activists said more than 50 people were killed in violence across the country Monday, mainly in the northern provinces of Aleppo and Idlib.
Since early Monday, shelling targeted areas in Idlib and Aleppo. An amateur video posted online by activists showed images of a man holding the body of a little girl who had been decapitated in the shelling.
Ongoing fighting in restive areas, meanwhile, prevented some schools from opening on the second day of the new school year, activists said.
The UN has estimated that more than 2,000 schools have been damaged or destroyed since the uprising in Syria began in March 2011.
Syrian jets on Monday attacked areas near the eastern Lebanese border with Syria, causing fear and panic among residents, a witness told dpa.
"The sound scared the people because they thought they were striking Lebanese areas, but the actual hit was inside Syrian territories just adjacent the border," a Lebanese border guard said.
Earlier, local television stations reported that Kherbet Daoud in Aarsal and Wadi al-Shehout, both in Lebanon's eastern Bekaa valley, were shelled by Syrian fighter jets.