Syria peace envoy Lakhdar Brahimi appealed to both sides to call a truce to the conflict during a Muslim holiday this week after talks with President Bashar al-Assad, as a deadly blast rocked Damascus.

The plea came as thousands of people demonstrated against the Syrian regime at the Beirut funeral of a top Lebanese police intelligence chief, killed in a car bomb which Lebanon's opposition has blamed on its neighbour.

In Syria's capital, a bomb exploded outside a police station in a Christian quarter of the Old City, killing 13 people, the state news agency SANA reported, blaming rebels.

It was the first such attack against a Christian quarter since the uprising against Assad's regime erupted 19 months ago.

"The blast was so strong that my house, a mile away, shook," one resident told AFP.

Many Syrian Christians -- who make up just five percent of the mostly Sunni Muslim population -- have sided with the regime, fearing that the uprising could trigger an Islamist backlash against their community.

The bombing came as UN-Arab League envoy Brahimi called for "unilateral" ceasefires by the regime and the rebels for the Eid al-Adha holiday, or Feast of Sacrifice, which starts Friday.

"I appeal to everyone to take a unilateral decision to cease hostilities on the occasion of Eid al-Adha and that this truce be respected from today or tomorrow," he said.

"This is a call to every Syrian, on the street, in the village, fighting in the regular army and its opponents, for them to take a unilateral decision to stop hostilities."

Although he stressed that the ceasefire call was his personal initiative, both UN chief Ban Ki-moon and the head of the Arab League Nabil al-Arabi have also backed the initiative.

Brahimi said he had contacted political opposition leaders inside and outside Syria and armed groups in the country. "We found them to be very favourable" to the idea of a truce, he said.

"We will return to Syria after the Eid (feast) and if calm really takes hold during the feast, we will continue to work" on ending the conflict, he added.

Assad, during his meeting with Brahimi, said he was "open to any sincere efforts seeking to find a political solution to the crisis based on respecting Syria's sovereignty and rejecting any foreign interference," SANA reported.

Brahimi also met Sunday with the ambassadors of Russia and China -- countries that have blocked resolutions for tough actions against Syria at the UN Security Council -- an AFP reporter said.

Brahimi has visited several countries with influence in the Syrian conflict over the past week, including Lebanon and Iran, warning that the violence could spread and set the entire region ablaze.

Such fears were compounded when a massive car bomb exploded on Friday in Beirut, killing three people including a senior police intelligence chief linked to the anti-Damascus camp in Lebanon, General Wissam al-Hassan.

Lebanon, which was under Syrian military and political domination for 30 years until 2005, has been divided over the conflict in Syria and has experienced violence between supporters and opponents of the Assad regime.

A nine-year-old girl was killed Sunday during clashes between supporters and opponents of the Syrian regime in the northern Lebanese city of Tripoli.

Although Syria joined international condemnation of the killings, Damascus has emerged as the prime suspect in Hassan's assassination.

After Sunday's Beirut funeral, Lebanese police tear-gassed demonstrators trying to storm the offices of Prime Minister Najib Mikati and demand his resignation over the killing.

On the ground in Syria, at least 125 people were killed in new violence, including 57 civilians, the Britain-based Syrian Observatory for Human Rights reported, adding to its estimate of more than 34,000 dead since March 2011.

Clashes were reported in the Damascus province town of Harasta and in the northern city of Aleppo, a key battleground for three months.

A car bomb exploded in Aleppo's Sarian district, wounding several people, an AFP correspondent said. A security source said the blast was caused by "a suicide car bomber".

Renewed fighting was also reported at the southern entrance to Maaret al-Numan, a strategic town on the Aleppo-Damascus highway that fell to the rebels on October 9, severing a key army supply route.

[Image via Agence France-Presse]