International peace envoy Lakhdar Brahimi appealed to Iran to help arrange a ceasefire in Syria during the Islamic holiday of Eid al-Adha as rebels and government forces fought street by street and village by village on Monday.
Brahimi made the request in talks with Iranian leaders on Sunday in Tehran, Syrian President Bashar al-Assad's closest regional ally in his campaign to crush a 19-month-old uprising.
The veteran Algerian diplomat said the civil war in Syria was getting worse by the day and stressed the urgent need to stop the bloodshed, his spokesman said on Monday.
He suggested the truce be held during the Eid holiday, which starts around October 25 and lasts several days. It would "help create an environment that would allow a political process to develop".
There was no immediate response from either side and with fighting raging on Monday in several Syrian cities and in the countryside, it was not clear if they would want to put the brakes on any battlefield advantages.
A ceasefire brokered by Brahimi's predecessor Kofi Annan in April fell apart after a few days and Annan later quit his job in frustration.
A senior United Nations political official, briefing the Security Council in New York, said that for any ceasefire to succeed, "this must be a collective effort by all inside Syria, in the region and beyond".
The official, Jeffrey Feltman, said all governments should stop supplying weapons and giving military assistance to any side in the conflict.
"Human rights abuses, including arbitrary detentions, torture and summary executions continue unabated. The voices of the peaceful protests that emerged so proudly last year have receded in the tremor of fighting," he said.
The conflict has claimed more than 30,000 lives since March 2011, when demonstrations first broke out calling for an end to the Assad family's dynastic rule.
The Syrian Observatory for Human Rights said 50 people had been killed across the country so far on Monday, nearly half of them soldiers. That followed a death toll of 170 on Sunday.
The pro-opposition Observatory said two rebel-held districts in northeast Aleppo, al-Shaar and Karm al-Jabal, came under heavy bombardment from Assad's forces on Monday. It also reported clashes in the district of Jdeideh, just north of the ancient citadel in Syria's biggest city.
Syrian television showed footage of soldiers inside Aleppo's Great Mosque, which dates back to the 8th century and was badly damaged in fighting between government forces and rebels battling for control of the Old City.
The mosque's medieval arches were charred, its elaborate wooden panels smashed and metal filigree lanterns lay broken in the courtyard. The sound of nearby gunfire could be heard.
In northwestern Idlib province, government warplanes bombed several towns on Monday, the Observatory said.
Rebels had surrounded an army garrison on Sunday close to a northwestern town in the latest push to seize more territory near the border with Turkey, opposition activists said.
Several hundred soldiers were trapped in the siege of a base in Urum al-Sughra, on the main road between Aleppo, Syria's commercial and industrial hub, and Turkey.
"Rebels attacked an armored column sent from Aleppo to rescue the 46th Regiment at Urum al-Sughra and stopped it in its tracks," Firas Fuleifel, one of the activists, told Reuters by phone from Idlib province, the main base and supply route for the insurgents fighting in Aleppo.
He said a jet was shot down while trying to provide air support to the column.
On the border with Turkey's Hatay province, the rebels appeared to have a tentative hold after four days of heavy fighting in the town of Azmarin and surrounding villages.
Giving an overview of the military situation, analyst Shashank Joshi of the Royal United Services Institute in London said the rebels, boosted by weapons from Gulf States and gaining in fighting skills, were possibly doing better. Assad's forces were increasingly stretched and taking more casualties.
On the other hand, opposition forces have not coalesced and formed a reliable chain of command connecting local groups.
"So even if government forces are losing their grip, what is taking over is many opposition groups," Joshi told Reuters. "I am less confident of regime collapse within six months than I was in July."
The rebels have made ground in Aleppo but not as much as they would have liked and at much higher cost, he said.
It would be important if the rebels are able to maintain their block of the north-south highway between Damascus and Aleppo but the lack of cover on the roads make them vulnerable to air strikes, he said.
If they can hold the road, the government's helicopter fleet would be strained as it would be diverted from an attack role by the need to resupply stranded towns.
The "game-changer" could be Turkey, once an ally of Assad and now a leader in international calls for him to quit, Joshi said.
Turkey's confrontation with Syria deepened in the past two weeks because of cross-border shelling and escalated on October 10 when Ankara forced down a Syrian airliner en route from Moscow, accusing it of carrying Russian munitions for Assad's military.
Ankara said in on Sunday it had closed Turkish air space to Syrian planes. Damascus also banned Turkish planes from flying over its territory.
Russia has said there were no weapons on the grounded plane and that it was carrying a non-legal cargo of radar. But it acted to cool friction with Ankara - Foreign Minister Sergei Lavrov said the incident would not hurt "solid" relations.
After meeting mediator Brahimi, Iranian Foreign Minister Ali Salehi said Iran was ready to work with him for peace and repeated Tehran's call for an immediate ceasefire before reforms and elections to resolve the conflict.
"We all need to join hands so that this conflict comes to a halt and further bloodshed is stopped," Salehi said.
Shi'ite Iran is the main ally in the region of Assad, who is a member of the Alawite sect, an offshoot of Shi'ite Islam.
The uprising has been led by the Sunni Muslim majority and is backed by Sunni-ruled Arab states and by Turkey, also led by a party with its roots in Sunni Islamist politics.
Turkey's disaster management agency said on Monday the number of Syrian refugees housed in camps in southern Turkey has exceeded 100,000, reaching the limits of its ability to cope.
Two other Syrian neighbors, Lebanon and Jordan, are sheltering 94,000 and 106,000 refugees respectively, according to the United Nations refugee agency.
(Additional reporting by Jonathon Burch on the Turkey-Syria border, Khaled Yacoub Oweis in Amman, Yeganeh Torbati and Zahra Hosseinian in Dubai and Oliver Holmes in Beirut; Editing by Jon Hemming)