A monitor and Syria's opposition have called for an investigation into a U.S.-led coalition strike last week that allegedly killed 64 civilians, nearly half of them children, in northern Syria.

The U.S. military on Sunday acknowledged coalition strikes in the Birmahle area but said it was unaware of any civilian deaths.

The U.N. will Tuesday start hosting separate talks with rival sides and "as many stakeholders as possible" in war-torn Syria in a bid to kickstart stalled negotiations to end the four-year conflict.

United Nations peace envoy for Syria Staffan de Mistura will give a news conference around midday Tuesday, kicking off four to six weeks of "separate consultations" with different sides in Syria's four-year conflict, spokesman Ahmad Fawzi said.

Progressive Socialist Party leader MP Walid Jumblat began on Monday his testimony at the Special Tribunal for Lebanon that is examining the assassination of former Prime Minister Rafik Hariri by recounting the nature of the ties between Lebanon and Syria, particularly with the ruling Assad family.

He told the trial chamber: “Bashar Assad showed hostility towards Rafik Hariri before he was elected president.”

Two U.N. peacekeepers were wounded on Monday when mortar rounds fired from Syria hit their base in the Israeli-held sector of the Golan Heights, an army spokesman said.

"Mortar shells hit the Golan in Ein Zivan and in the Zivanit UNDOF base. Two U.N. peacekeeping soldiers were evacuated to Israel for medical care," Lieutenant Colonel Peter Lerner wrote on his official Twitter account.

Hizbullah chief Sayyed Hassan Nasrallah is expected to make a televised speech on Tuesday to tackle the latest local and regional developments.

Nasrallah will deliver his speech around 8:30 pm.

Gunmen entrenched on the outskirts of the eastern Lebanese border reportedly withdrew from their positions as the Lebanese army denied involvement in a gunbattle outside the country's border.

“Information obtained during the past two days indicates that gunmen withdrew in a limited manner from posts controlled on the outskirts,” a source close to Hizbullah said in comments published in An Nahar newspaper on Monday.

The U.S. military denied Sunday a report that strikes led by Washington had killed at least 52 civilians in northern Syria earlier this week, saying those killed were actually fighters.

Syrian Observatory for Human Rights monitor director Rami Abdel Rahman had told Agence France Presse that seven children were among the dead from U.S.-led coalition strikes overnight Thursday into Friday on the village of Birmahle in Aleppo province.

The U.N.'s cultural body on Sunday awarded its annual press freedom prize to Mazen Darwish, a Syrian journalist and rights activist who has been jailed by the regime for more than three years.

Darwish was arrested on February 16, 2012 along with Hani Zaitani and Hussein Ghreir, his colleagues at the Syrian Center for Media and Freedom of Expression. They are accused of "promoting terrorist acts."

Syria's army cut the last main supply route for a rebel bastion east of Damascus Sunday, further tightening a crippling siege on the area, a monitor and state media said. 

"The regime has cut off the last main road for rebels leading out of Eastern Ghouta," the main opposition stronghold in Damascus province, said Syrian Observatory for Human Rights chief Rami Abdel Rahman. 

The Lebanese army is reportedly mobilizing troops in preparation for a possible battle along the border near the strategic Syrian town of Qalamoun.

Speaker Nabih Berri stressed on Sunday in comments published in the pan Arab daily al-Hayat that Hizbullah should engage in the Qalamoun battle alongside the Lebanese army.