BEIRUT — Syrian rebels fully captured a northern town near the Turkish border on Tuesday after weeks of heavy fighting and attacked a regime air base in a neighboring province, activists said.
The air base is in Aleppo Province, where opposition fighters have already captured three large military bases in recent months. Rebels have also laid siege to the international airport in the city of Aleppo, Syria’s commercial capital, and launched an offensive on the police academy near the city.
With steady rebel gains across the north, President Bashar Assad’s regime is having increasing difficulty sending supplies by land to Aleppo Province, especially after rebels cut a major thoroughfare from Damascus.
It is just another sign that the opposition is consolidating its grip across large swathes of territory in northern Syria near the Turkish border.
In another blow to the Assad government, activists said that Mohammed Adnan Arabo, a member of Syria’s Parliament, has left the country and joined the opposition. Ahmad Ramadan, an executive council member of the opposition Syrian National Council group, and other activists said Arabo arrived in Turkey on Tuesday.
He said the government’s hold on power is deteriorating and rebels are besieging military bases for weeks until they either take over or negotiate with local army commanders to surrender. He added that some regime forces are being diverted to the capital to fight there.
‘‘The regime cannot protect its bases and also cannot send forces to support troops under siege,’’ he said.
Over the weeks, rebels fighting to overthrow Assad have also been able to take the battle into the capital Damascus, Assad’s seat of power, where the southern neighborhoods are witnessing almost daily clashes between troops and rebels.
The big successes began in mid-November, when rebels captured Aleppo’s Regiment 46, a large military base, carting off tanks, armored vehicles, and truck-loads of munitions. Three weeks later, they captured the Sheik Suleiman base near the provincial capital of Aleppo, and days later they took an infantry base in the city.
Last week, they captured an army technical regiment near Damascus international airport but were pushed back in a counterattack. The army command said in a statement that the regiment’s commander was killed in the battle.
The rebels have also brought the battle to areas around Damascus international airport where some flights were canceled earlier this month because of the intensity of the fighting.
One of the biggest blows came in Damascus on Dec. 12 when a suicide attacker blew up his vehicle outside the Interior Ministry, killing five and wounding many, including Interior Minister Mohammed al-Shaar. The government denied at first that Shaar had been wounded until it got out when he was taken last week to a Beirut hospital for treatment.
It was the second injury the minister suffered after being wounded in a July 17 bombing inside a high-level crisis meeting in Damascus that killed four top regime officials, including Assad’s brother-in-law and the defense minister.
The rebel takeover of Harem, a town of 20,000 in northern Idlib province, was the latest in a string of recent rebel successes.
The Britain-based Syrian Observatory for Human Rights said the rebels captured Harem in the early hours of Tuesday. Mohammed Kanaan, an Idlib-based activist, said the last post to be taken was the historic citadel, which overlooked the town. The army had turned the citadel into a military post.
‘‘Harem is fully liberated now,’’ Kanaan said via Skype. He added that as the rebels pounded army posts and checkpoints in Harem, the troops withdrew to the citadel that later fell in the hands of rebels.
Rami-Abdul-Rahman, who heads the Observatory, said nearly 30 soldiers and pro-government gunmen surrendered late Monday. He added that rebels set free all gunmen 16 or younger and referred others to local tribunals.
‘‘Harem was very important because it is one of the towns that was loyal to the regime,’’ Abdul-Rahman said by telephone about the town that is nearly a mile from the Turkish border.
In Aleppo Province, which neighbors Idlib, local activist Mohammed Saeed said rebels attacked the air base in the town of Mannagh near the Turkish border.
He said it is one of four air bases in the province, adding that rebels also attacked the police academy near the city of Aleppo.
Government forces have been using helicopters to carry supplies to besieged areas and to attack rebel positions.
The regime has had increasing difficulty sending supplies by land to Aleppo Province after rebels captured in October the strategic town Maaret al-Numan.