Rebel fighters in Syria are closing in on a key airport in Aleppo used by the government to transport soldiers and supplies to its war effort in northern Syria.
On Tuesday, Syrian government forces rushed hundreds of soldiers from army bases south of the city to Aleppo's international airport in order to halt the rebels' advance.
A Syrian military source told Agence France-Presse that fighters made an incursion into the airport's fuel warehouse on Monday but were later forced back in a government counterattack.
Control of the airport, the second-largest in Syria, is vital for the regime as it is the chief supply line to government forces in the country's north. Should the government lose control of the airport, it would lose its only remaining means of getting food, arms, ammunition and other supplies to soldiers upholding its presence in Aleppo. Government forces inside the city centre have only managed to stop rebels overrunning Aleppo through a steady stream of logistical support the airport allows them to receive.
For rebels, taking the airport would be a hugely symbolic victory. One fighter told the BBC it would mean "wiping out the Syrian army in Aleppo." But the forces fighting to oust President Bashar al-Assad have been unable to use fighter aircraft or the advanced military hardware looted in past assaults on military bases.
Following a series of rebel victories in southeast Aleppo recently, only the Nairab military air base, a major installation adjacent to the international airport, stands between the fighters and the strategic gateway that is their prize. On Tuesday, BBC reporters accompanying fighters, led by Islamist groups including Jabhat al-Nusra, posted pictures to Twitter of idle commercial airplanes at the international airport.
Edward Dark, the pseudonym of an anonymous activist who has been based in Aleppo since the beginning of the revolt, said in an e-mail interview that the airport is heavily defended, "so it's not clear if rebels will be able to capture it. If they do, it will be a huge blow in terms of getting supplies and equipment to the regime forces in Aleppo."
Mr. Dark said there have been no commercial flights in or out of the airport for six weeks since rebels in the area began targeting civilian jets with anti-aircraft gunfire.
Rami Abdul-Rahman of the Syrian Observatory for Human Rights, an opposition group based in Britain, said the government does not use the airport for its fighter jets and military helicopters. "But if the rebels can control Nairab [air base], the regime will not be able to defend the international airport," he added.
Syrian army forces and rebels have been fighting for control of Aleppo and its suburbs since July with neither side able to land a knockout blow. Rebel fighters had been unable to get close to the airport until earlier this month when they took control of the Sheikh Saad district in the city's southeast by overrunning a major government checkpoint.
Since then, advances toward the international airport have been swift. Small air bases, including al-Jarrah, Hassel and Base 80, as well as another checkpoint near the airport, have been seized in the past week.
Rebel fighters in Aleppo are broadly divided into two groups. Fighters operating under the Free Syrian Army title have long been bogged down in fighting with regime soldiers in the city's inner neighbourhoods. Separately, Islamist-leaning groups led by Jabhat al-Nusra – designated a terrorist group by the United States – have been successful in taking government air bases and checkpoints in the city's suburbs.
A blast in the rebel-held Jabal Bedro district of Aleppo killed at least 20 people on Tuesday, many of them children, in what is thought to have been a surface-to-surface missile attack.
Activists have accused the government of firing Russian-made Scud missiles on areas where rebels are known to operate in the past, including in an attack on Aleppo University last month. The use of such weapons shows Damascus facing an increasingly desperate situation by losing the ground war against its opponents.
In Damascus, the state-run news agency, SANA, said two mortars exploded near a presidential palace in the west of the city.
No casualties were reported and it was unclear whether Mr. al-Assad was in the palace. He has two other official residences located close byin the capital.
The attack was the first close to a presidential palace to be confirmed by state media and another sign that the civil war is seeping into areas of the capital once considered safe.
"This is a clear message to the regime that nowhere is safe from now on," Khaled al-Shami, an activist in Damascus told the Associated Press. "The fact that they had to announce it means they can no longer hide what is happening in Damascus."
The news service, SANA, said "terrorists" fired the rounds that struck near the southern wall of the Tishreen palace in the capital's northwestern Muhajareen district. The government refers to anti-government fighters as "terrorists."