Syria conflict: Fighting rages at Syria air bases
Rebels and regime forces have been battling for control of several air bases in Syria.
The government said it had repelled a huge attack on an air base near Aleppo while rebels claimed victory in another battle in the east of the country.
The rebels have increasingly targeted the air force in recent weeks, accusing it of launching attacks on cities with helicopter gunships and fighter jets.
Meanwhile, Algerian Lakhdar Brahimi has taken up his post of UN peace envoy.
Mr Brahimi, who took over from Kofi Annan, has sought to play down expectations for his mission.
UN Secretary General Ban Ki-moon has been lobbying international leaders for support, saying he "believes in the power of diplomacy".
The BBC's Jim Muir in neighbouring Lebanon says there is no sign of a change of heart by either party within Syria, or their outside supporters.
He says conditions will have to change before Mr Brahimi can step in with a political solution that might actually work.
The humanitarian emergency on the country's borders is also intensifying, with Jordan saying it is struggling to cope with the influx of refugees.
On Saturday, Jordan and the UN's refugee agency issued a joint appeal for $700m (£440m) to deal with the crisis.
Jordan houses more than 180,000 Syrians who have fled the fighting, says the BBC's Dale Gavlak, in Amman.
State TV has been leading its bulletins with a report from the Rasm al-Abboud air force college near Aleppo, where it said government forces had repelled a sustained rebel assault.
The pro-rebel Syrian Observatory for Human Rights and other activists said government troops had been killed and wounded in the attack.
There are also reports by activists of prolonged fighting at the Abu Zohur air base in Idlib province.
And another air-force building in the eastern city of Deir al-Zour was seized, its commander killed and at least 16 personnel captured, the Observatory said.
Footage posted on the internet by activists showed captured regime officers and seized weaponry.
It is impossible to independently verify the claims, as reporting by foreign journalists is severely restricted in Syria.
But accounts from a number of people say battles have continued in Aleppo, suburbs of Damascus and other parts of the country.
Russia said on Saturday that calls by the UN and Western governments for the regime to stop using heavy weapons were naive.
"No matter your view of the Syrian regime, it is completely unrealistic in the current situation, when there is fighting in the cities, to say that the only way out is the unilateral capitulation of one of the opposing sides," said Foreign Minister Sergei Lavrov.
Russia and Iran are Syria's key international allies.
Syrian Prime Minister Wail al-Halqi held talks earlier with Iranian Supreme Leader Ayatollah Ali Khamenei and President Mahmoud Ahmadinejad.
Both assured him of Iran's continuing support in fighting what it agrees is a US and Israeli-backed campaign to undermine Syria because of its resistance to Israel.
The meetings came during a summit of the Non-Aligned Movement in Tehran.
Iran has been solid in its support for the Assad government.
But days earlier at the summit, Egyptian President Mohammed Mursi described the Syrian uprising as a "revolution against an oppressive regime", prompting a walkout by the Syrian delegation.