Insurgents fired mortar rounds at one of President Bashar al-Assad's palaces in the Syrian capital on Tuesday, as the death toll mounted from a devastating missile strike on second city Aleppo.

The shelling, which was claimed by the rebel Free Syrian Army, came as dozens of Russians left the war-battered country on a plane sent from Moscow as its navy reportedly dispatched four warships to the Mediterranean for a larger evacuation.

In Damascus, two mortar shells crashed into an area "near the southern wall of Tishreen palace" and two hospitals, causing damage but no casualties, state news agency SANA quoted an unnamed official as saying.

Little is known about Assad's movements, and Tishreen in west Damascus is normally reserved for dignitaries, but it was the first time his regime has reported shells falling near a palace since the 23-month conflict flared.

The rebel Free Syrian Army said its fighters had "fired mortars at the Tishreen presidential palace," one of three in the capital along with palaces at Mount Qassioun and Rawda.

The shelling came a day after an apparent surface-to-surface missile attack flattened a residential area of Aleppo city, killing at least 31 people, said the Syrian Observatory for Human Rights.

Fourteen children and five women were among the dead, it said, adding the toll was likely to rise as bodies were still under rubble and people were critically injured.

There were no planes overhead when the missile hit, according to residents, and the extent of the destruction indicated a surface-to-surface missile was likely used, the Observatory's Rami Abdel Rahman told AFP.

Abu Hisham, an Aleppo-based citizen journalist, said "housing in the district was informally built. It took one surface-to-surface rocket to destroy an entire neighbourhood."

Video footage and photographs shot by activists in Aleppo, scene of fierce fighting since the army launched an all-out assault to stop a rebel advance on the city on July 20, showed massive destruction in Jabal Badro.

Amateur film posted online by the anti-regime Aleppo Media Centre showed crowds of people gathering around hills of rubble and a bulldozer shovelling the debris as residents searched for loved ones.

"I swear to God! I rescued a baby aged just two months from the rubble!" an unidentified man cried out in the video, whose authenticity AFP could not verify.

In the regime stronghold of Latakia, two Russian government planes carried humanitarian aid from Moscow to the port city, before taking back 99 Russians and other ex-Soviet citizens who wanted to leave on their return trip.

Moscow, which unlike other world powers still keeps close ties with the Assad regime, also announced it would host Syrian Foreign Minister Walid al-Muallem for talks on the crisis next week.

On February 13, a top Russian official said Syria's opposition chief Moaz al-Khatib was also due in Moscow, though he did not specify when.

Observers are watching for any hints of Russia planning a full-scale evacuation of its citizens, which would be seen as a tacit admission from Moscow that Assad is doomed in his fight against rebels.

Meanwhile, hundreds of troops backed by military vehicles poured into Aleppo province, as rebels clashed with loyalists around Kwayris military airport as they pushed on with an assault to take control of Aleppo international airport.

At least 100 people were killed across Syrian on Tuesday, among them 58 civilians, 23 soldiers and 19 rebels, said the Observatory, which relies on a network of sources on the ground for its information

The latest violence came as the United Nations said more than four million people in Syria are in desperate need of aid, up sharply from 2.5 million in September.

"We are watching a humanitarian tragedy unfold before our eyes," said Valerie Amos, the UN under-secretary-general for humanitarian affairs and emergency relief coordinator.

The UN says at least 70,000 people have been killed in the near two-year conflict, and puts the number of Syrians who have fled their homeland at more than 850,000.

Rebels down Syria warplane as air raid kills 14: NGO
Beirut (AFP) Feb 20, 2013 - Syrian rebels downed a warplane over Hammuriyeh on Wednesday, shortly after an air strike killed at least 14 people and wounded dozens more in the Damascus province town, a watchdog and activists said.

Amateur video shot by activists and distributed by the Syrian Observatory for Human Rights showed a warplane firing from the sky and then going down in flames after apparently being hit.

"It's gone up in flames! Allahu akbar (God is greatest)! The (rebel) Free Syrian Army air defence battalions have hit a MiG warplane!" cried the cameraman filming the video.

Lacking sophisticated weaponry, rebels fighting President Bashar al-Assad's regime have frequently used heavy machineguns to shoot down warplanes deployed to strike insurgent enclaves across the country.

"The shelling and bombardment in Eastern Ghuta province on Wednesday was fierce," Observatory director Rami Abdel Rahman told AFP, adding that the warplane was shot down as it was bombarding the town.

The air strike killed 12 men, a woman and a child, said the Britain-based watchdog which relies on a network of activists, medics and lawyers on the ground for its information.

A video filmed by activists in Hammuriyeh and distributed on Facebook showed residents in the aftermath of the strike pouring water on a burning corpse on the ground, and another two in destroyed vehicles.

The video, which AFP is unable to verify, also showed a lorry on fire and widespread destruction in the area.

Elsewhere, clashes raged between rebels and troops in the northern province of Aleppo, days after rebels launched an assault to seize the international airport and other air bases in the region.

"The clashes around Kwayris military airport were fierce today, and there were also intermittent battles around Aleppo international airport and Nayrab military air base," said Abdel Rahman.

Activists say the rebels' assault is aimed at stopping warplanes from taking off, and at seizing ammunition, while rebels say it is part of a bid to expel troops from the north.

In the past week, rebels have captured air bases at Al-Jarrah, Hassel and Base 80, as well as an important checkpoint near the international airport.

"When the Free Syrian Army manages to free all the border crossings in the north and the airports in Aleppo, the area will fall completely out of regime control," rebel commander in the northern province, Colonel Abdel Jabbar al-Okaidi, told AFP by phone.

"But as you saw on Monday night, the army is keen to take revenge against the Syrian people," he added, referring to a powerful missile strike on the Aleppo district of Jabal Badro that killed at least 33 people, according to the latest Observatory count.

The UN says more than 70,000 people have been killed in Syria's nearly two-year war, most of them civilians.

According to a preliminary toll by the Observatory at least 107 people were killed in violence across Syria on Wednesday, among them 54 civilians.