* Turkish forces, allies try to storm Afrin town, YPG says
* Russia, Iran, Turkey convene meeting on Syria in Astana
Thousands of civilians were fleeing from besieged enclaves on opposite ends of Syria on Friday as two major battles in the multi-sided war entered decisive phases, with hundreds of thousands of people trapped in the path of both assaults.
Air strikes killed scores of people in eastern Ghouta, a war monitor said, and weary residents streamed out on foot for a second day, as Russian-backed government forces pressed their campaign to capture the last big rebel bastion near Damascus.
On another front, Turkish and allied rebel forces shelled the northern Kurdish-held town of Afrin heavily, killing at least 27 people and forcing 2,500 people to flee, the Syrian Observatory for Human Rights war monitor reported.
The Kurdish YPG militia defending Afrin said it was battling the Turkish forces who tried to storm the town from the north.
The two offensives, one backed by Russia and the other led by Turkey, have shown how Syrian factions and their foreign allies are aggressively reshaping the map of control after the defeat of Islamic State's self-proclaimed caliphate last year.
The Syrian war entered its eighth year this week having killed half a million people and driven more than 11 million from their homes, including nearly 6 million who have fled abroad in one of the worst refugee crises of modern times.
The government launched its offensive on eastern Ghouta a month ago, and Turkey began its cross-border assault in Afrin in January. In both cases, hundreds of thousands of civilians have been trapped inside encircled pockets on the battlefield.
Air strikes kill 57, civilians flee
Backed by Russia and Iran, government forces have thrust deep into eastern Ghouta on the capital's outskirts, splintering the rebel enclave into three separate zones. The United Nations believes up to 400,000 people have been trapped in the densely populated farms and satellite towns, short of food and medicine.
For the first time in the month since the government unleashed the Ghouta offensive, one of the deadliest of the war, residents are fleeing in their thousands, carrying children and belongings on foot from rebel territory to government positions.
Moscow and Damascus accuse the rebels of having forced people to stay in harm's way as human shields. The rebels deny this and say the government aims to depopulate opposition areas.
The Observatory said air strikes in eastern Ghouta killed 64 people, including 13 children, in the town of Kafr Batna and another 12 people nearby on Friday. It said Russian aircraft had carried out the strikes. Syrians believe they can distinguish Russian aircraft from those of the Syrian army because the Russians fly at higher altitude.
Syrian State TV broadcast footage of men, women and children walking along a dirt road near the town of Hammouriyeh, many of them carrying bags, to escape rebel towns. Some waved to the camera and said the rebels had stopped them from leaving.
Russian news agencies reported that more than 4,000 people had come out on Friday.
A humanitarian spokeswoman for the United Nations in Damascus said the actual number of people who had exited eastern Ghouta so far was not known and neither were the destinations of all evacuees. The U.N. had not observed the evacuations, but was visiting shelters where some of the people were arriving.
The Istanbul-based spokesman for Failaq al-Rahman, the rebel faction controling the pocket that has seen the exodus, has said civilians' safety could not be guaranteed in government areas.
The mayor of the nearby army-held town of Adra, Jassem al-Mahmoud, said around 5,000 people were sheltering there so far and as many as 50,000 were expected, who would be guaranteed food and medical help.
The U.N. children's fund UNICEF said it had response plans in place to cope with 50,000 people leaving eastern Ghouta.
The outflow began on Thursday with thousands fleeing the southernmost of the three Ghouta pockets. Russia said more than 12,000 people left on Thursday.
During campaigns to recover other areas, the Syrian government has taken territory by allowing rebel fighters and opposition activists safe passage out to insurgent-held areas at the Turkish border. Russia has offered similar safe passage to rebels who leave eastern Ghouta, but so far they have refused.
Alarming reports
The Ghouta and Afrin campaigns have both continued despite a UN Security Council demand for a 30-day ceasefire. Moscow and Damascus argue the rebels they target in Ghouta are terrorists unprotected by the truce. Turkey says the same of the Kurdish YPG militia it is fighting in Afrin.
The foreign ministers of Turkey, Iran and Russia convened a meeting in the Kazakh capital Astana to discuss the situation in Syria. The three states last year agreed to contain the conflict on several fronts with "de-escalation zones", while simultaneously pursuing own military objectives in Syria.
Turkey wants to crush the YPG which it views as an extension of the Kurdistan Workers' Party (PKK), which has waged an insurgency in Turkey. The United States views the YPG as a valuable partner in its war against Islamic State in Syria.
A spokeswoman for the UN human rights office said it had received "deeply alarming reports" of civilians being killed and injured in air strikes and shelling in Afrin, and of the Kurds preventing civilians from leaving.
Lebanon's Al-Mayadeen TV broadcast footage from the Afrin area showing cars, small trucks, tractors and groups of people on foot leaving the town. An elderly man told the channel he had left on foot at 2 a.m. when shells started falling.
"There are a lot of people leaving the city as well, and a lot still inside," he said.
President Tayyip Erdogan said Turkey had "largely solved the Afrin issue". "We are nearing the end in Afrin," he said.
