BEIRUT/DAMASCUS: Battles raged Thursday around a strategic main airport and a military air base in northern Syria as rebels and government forces try to secure control of territory along the Turkish border, activists and military sources said.

Insurgents besieged troops on the perimeter of the international airport in Aleppo, the hard fought-over principal city of Syria’s north, and an air force base near Idlib province, the opposition-aligned Syrian Observatory for Human Rights said.

Aleppo airport has been closed since Tuesday after repeated attacks by rebels, according to an airport official, who said it would reopen as soon as the army regained control of the surrounding area.

Rebels holding swathes of the north were targeted by regime shelling overnight in Aleppo’s Sakhur district and in the towns of Marea and Azaz farther north near the Turkish border

In the northwestern province of Idlib, hundreds of fighters of two hard-line Islamist rebel groups, the Nusra Front and Ahrar al-Sham, fought soldiers around the Taftanaz air base, rebels in the area and the British-based Observatory said, adding that airstrikes were blasting rebel positions.

The rebels had remotely detonated a bomb at one of the air base’s gates the day before but were pushed back by the army, according to both the Observatory and a military source inside the base.

The military source told AFP that the clashes outside the base had been continuing non-stop for over 48 hours and that there had been a large number of rebel casualties.

Rebels and opposition activists released footage on YouTube purportedly showing a government tank exploding inside the base from rebel positions on the perimeter.

Footage is nearly impossible to verify as Syria bans most foreign journalists from entering the country.

Rebels and opposition activists in nearby Binnish told The Daily Star government MiG planes were shelling the northern part of the city and rebel positions on the road to Taftanaz. As the activist spoke via Skype, large explosions could be heard in the background.

The rebels have been pursuing a strategy of attacking airports and military airfields, targeting five air bases in Idlib and the nearby province of Aleppo, trying to chip away at the government’s air power, which poses the biggest obstacle to advances by opposition fighters.

The government has increasingly relied on its warplanes and helicopters to target opposition forces.

The Taftanaz air base is considered strategically important as it is one of two northern helicopter bases that rebels say is used to launch shelling campaigns across the north and provide air cover to government military convoys traveling along main arteries in the region.

In eastern Syria Thursday, three rebels were killed in combat with troops around the Deir al-Zor military airport, as fighting also broke out in the nearby provincial capital.

Rebels there claimed to have shot down a government MiG plane.

Footage released on YouTube showed rebels celebrating and what appeared to be a plane spiraling toward the ground after apparently being targeted by a rebel anti-aircraft gun. In the town of Mleha, just east of Damascus, bodies were being recovered from a service station hit by a regime airstrike Wednesday.

The toll from the attack was not yet known, but the Observatory said at least 12 bodies had been recovered, several of them rebels. The Local Coordination Committees, a grassroots network of activists, estimated at least 50 people were killed.

The Observatory said 219 people died Wednesday nationwide – 115 civilians, 57 rebels and 47 soldiers.

Thursday’s violence killed at least 39 people nationwide, most of them civilians, the Observatory said in an early count that was likely to rise overnight.

On the aid front, a 33-truck aid convoy organized by Turkish and Qatari relief groups left Istanbul for Syria Thursday carrying 850 tons of flour.

“Assad’s regime is bombing the bakeries and there is a very huge need for flour in Syria,” Huseyin Oruc, the vice president of Turkish IHH Humanitarian Relief Foundation, said.

The overall death toll of the 21-month Syrian conflict has unsettled observers.

The U.N. High Commissioner for Human Rights Navi Pillay Wednesday called it “truly shocking” as she revealed a vetted U.N. tally nearly a third higher than that previously compiled by the Observatory.

“Given there has been no let-up in the conflict since the end of November, we can assume that more than 60,000 people have been killed by the beginning of 2013,” Pillay said.

The average number of deaths recorded in recent months was five times that registered mid-2011, reflecting intensifying viciousness and an increased resort by the government to airstrikes.

Pillay said in her statement that “this massive loss of life could have been avoided” if the government of President Bashar Assad had not chosen the “ruthless suppression” of what initially were peaceful protests.

U.N.-Arab League peace envoy Lakhdar Brahimi warned over the weekend that Damascus faced a choice between “hell or the political process.”

Karim Bitar, an analyst at the Paris-based Institute for International and Strategic Relations, was skeptical the new U.N. toll would have a political impact.

“The world has become unfortunately so toughened to these figures, sort of anaesthetized. There is this terrible Stalin quote: ‘One death is a tragedy; one million is a statistic,’” he said.