Syrian rebels on Thursday shelled an air base being used by regime forces to pound the northern city of Aleppo, as a rights watchdog reported 43 people killed in a raid near Damascus.
"Menagh military airport was bombarded on Thursday morning by a tank captured previously by the rebels," the Syrian Observatory for Human Rights said of the base 30 kilometres (18 miles) northwest of the country's commercial capital.
An AFP reporter who witnessed the bombardment said rebels told him it was "an attack to take this airport being used by helicopters and planes that are firing on Aleppo."
The United Nations confirmed on Wednesday that rebels battling President Bashar al-Assad's regime now had heavy armour, and that its military observers had seen the Syrian military use a fighter jet to attack rebels in Aleppo.
AFP correspondents on the ground have reported that rebels have captured a number of tanks, and some armoured units have defected with their vehicles.
It is difficult to get an overall picture of the situation inside Aleppo itself because of a lack of independent sources and restrictions on journalists.
The Observatory and an activist said mobile phone and internet services in Aleppo have been cut since Wednesday, and a security source in Damascus told AFP such cuts are "generally the precursor to a major military offensive."
Thursday's air base assault comes after US President Barack Obama was reported to have signed a covert document authorising US support for the rebels.
The directive was contained in a "finding" -- a device authorising clandestine action by the Central Intelligence Agency, NBC and CNN said, citing unidentified sources.
White House officials declined to comment, but did not specifically rule out the idea that Washington was providing more intelligence support to anti-Assad forces than had previously been made public.
US defence secretary Leon Panetta was in Jordan on Thursday for talks on Syria.
"Both of our nations share concerns about what is happening in Syria and the impact that that could have on regional stability," he told reporters.
The Observatory said a security forces raid southwest of Damascus killed 43 people, some of whom were tortured and executed.
"Regime forces entered the Jdaidet Artuz district on Wednesday and arrested around 100 young people who were taken to a school and tortured," it said.
"On Thursday morning after the operation the bodies of 43 people were recovered. Some of them had been summarily executed."
The Observatory had reported on Wednesday 28 civilians killed in the raid.
A resident of neighbouring Artuz said the army had shelled the village from Jdaidet Artuz.
"There's nobody. Not one shop is open the houses have been deserted by their inhabitants fearing violence -- everyone has fled," the resident said.
Pro-regime newspaper Al-Watan on Thursday said security forces were "hunting down terrorist groups" in Damascus province.
Nationwide, 163 people were killed on Wednesday -- 98 civilians, 20 rebels and 45 soldiers -- said the Observatory, which has estimated that more than 20,000 people have died since mid-March last year.
Assad said on Wednesday the army was fighting for Syria's future.
"The army is engaged in a crucial and heroic battle... on which the destiny of the nation and its people rests," the official SANA news agency quoted him as saying in a speech marking armed forces day.