Rebel fighters near Syria's city of Aleppo have attacked a key army base, using a tank seized from the military.
The rebels say they bombarded the base to the north of Aleppo, which had been used to launch artillery and air strikes on rebel positions in the city.
In Damascus, government forces launched two operations to root out rebel activists on Wednesday, killing at least 70, the opposition has said.
Troops reportedly went from house to house demanding to see people's papers.
Activists say the soldiers summarily executed many of their victims.
Syrian state TV said "dozens of terrorists" surrendered or were killed in the operation.
Opposition commanders in Aleppo said they used a tank captured from the army to bombard the Menagh air base, which lies between Aleppo and the rebel-held town of Azaz near the Turkish border.
Their claim was backed up by the London-based Syrian Observatory for Human Rights and an AFP news agency reporter.
The commanders said government forces had been using the air base as a staging post for attacks on nearby areas.
It is one of the first uses of heavy weaponry by the rebels in the city, who are heavily outgunned by the military.
The fighting in Aleppo city appears to have settled into a stalemate.
State TV, which had initially forecast that the city would be cleared of rebel fighters in just a few days, is now reporting only a few clashes with "terrorist mercenaries".
On Wednesday, a prominent member of the opposition Syrian National Council, Burhan Ghalioun, who is in Paris, said they would "automatically" establish a headquarters in Aleppo if the city fell to the rebels.
"There will be nothing more that will stand in the way of the Free Syrian Army. Hama, Homs to the outskirts of Damascus have in large part been liberated," he said.
But the tactics used by some of the rebels are proving controversial.
Video posted online shows rebel gunmen killing several prisoners who were said to belong to a pro-government militia in the city of Aleppo.
The prisoners, some of them bruised and bloodied, were put up against a wall half-naked and shot with Kalashnikov rifles.
The opposition Syrian National Council has criticised rebels, and Human Rights Watch has said the incident could be a war crime.
In other developments:
- Syrian soldiers fired on Jordanian troops who were waiting to take in refugees at the border, according to Jordanian officials
- US media report that President Obama approved an order earlier this year allowing the CIA and other agencies to aid the rebels
- Russian President Vladimir Putin is visiting the UK on Thursday and is expected to discuss the Syrian crisis with Prime Minister David Cameron
- The UN's Food and Agricultural Organization (FAO) says almost three million Syrians need help with food and farming
Witnesses and activists described heavy shelling and a ground assault on Wednesday in Damascus's south-western suburb of Jdeidet Artouz.
One resident told Reuters news agency the soldiers had inspected his ID, and then let him go.
He later saw bodies of at least 35 men.
"Almost all of them were executed with bullets to their face, head and neck," said the man, who identified himself as Fares.
On Thursday, the Syrian Observatory for Human Rights published a more detailed account of the assault, saying pro-government forces arrested about 100 people and tortured them.
"On Thursday morning after the operation, the bodies of 43 people were recovered. Some of them had been summarily executed," the organisation said in a statement.
Other activist groups gave higher figures for the number of deaths.
An army spokesman told state TV that a number of armed men had clashed with government forces who had raided a farm.
Another regime assault on the southern Damascus suburb of Yalda also resulted in the deaths of at least 27 people, activists said, without providing any further details.
Activists estimate some 20,000 people have died since anti-government protests erupted in March last year.