Syrian regime forces have launched new air strikes in what is seen as a desperate attempt to reverse rebel gains, as the opposition blamed the international community for fuelling Islamic extremism.
Reacting after Washington urged Syria's rebels to reject extremism, the head of the main opposition Syrian National Council said the West and its partners were to blame for rising radicalisation.
'The international community is responsible, through its lack of support for the Syrian people, for the growth of extremism in Syria,' SNC director Abdel Basset Saida told AFP.
'The international community should criticise itself, and ask itself: What did it give the Syrian people? How has it helped the Syrians to stop the regime's crazy killing?' he said.
Thursday saw helicopter gunships strafing a district of Damascus as warplanes pounded rebel bastions in the capital's suburbs and in the northwestern province of Idlib, said the Syrian Observatory for Human Rights.
At least three warplane raids were conducted in the northern Damascus suburb of Harasta, home to some of the rebel Free Syrian Army's best organised fighters, as on the other side of the city gunships hit the neighbourhood of Al-Hajar Al-Aswad, it said.
Clashes meanwhile raged in the northern commercial hub of Aleppo, it said, and in Idlib, where FSA forces backed by the Islamist Al-Nusra Front continued their siege of the Wadi Daif army base.
President Bashar al-Assad's forces have this week launched a wave of intensive air strikes analysts say are a response to opposition gains and aimed at 'terrorising' and turning local communities against the rebels.
'They are trying to make the civilian population so angry and so scared that it will not be possible for the rebels to find safe havens,' said Riad Kahwaji, head of the Dubai-based Institute for Near East and Gulf Military Analysis.
The air raids - often using crude barrel bombs stuffed with dynamite and chunks of metal - were not precision strikes on rebel positions but indiscriminate attacks on civilian areas under rebel control.
'These are dumb bombs, not smart bombs, and when you are using them you are not trying to gain any tactical advantage,' said Kahwaji.
Violence on Wednesday killed at least 152 people across Syria, including 58 civilians, said the Observatory.
It says more than 36,000 people have now been killed since the uprising against Assad's regime broke out in March 2011 and evolved into an armed civil conflict.
Most of the rebels, like the population, are members of Syria's Sunni Muslim majority, while Assad's government is dominated by his Alawite minority, an offshoot of Shi'ite Islam.
The country's fractured opposition, whose members range from pro-Western liberals to hardline Islamists, has struggled to find common ground against Assad, especially on the political front.
US Secretary of State Hillary Clinton on Wednesday said Washington wanted to help the Syrian opposition unite against Assad, but warned against Islamic extremists trying to 'hijack' the revolution.
'There are disturbing reports of extremists going into Syria attempting to take over what has been a legitimate revolution against an oppressive regime for their own purposes,' Clinton warned during a visit to Croatia.
The opposition should 'strongly resist the efforts by the extremists to hijack the Syrian revolution,' she said.
The international community's divisions over the conflict were exposed once more on Wednesday, as UN-Arab League peace envoy Lakhdar Brahimi urged China to do more to help tackle the crisis and talks between French and Russian officials in Paris failed to resolve disagreements over Assad's regime.
After the talks, Russian Foreign Minister Sergei Lavrov defiantly accused the West of fuelling the violence by insisting on Assad abandoning power.
'If the position of our partners remains the departure of this leader who they do not like, the bloodbath will continue,' Lavrov said.
Brahimi, who visited Moscow and Beijing this week in bid to revive peace efforts after a failed ceasefire bid for last weekend's Eid al-Adha Muslim holiday, is due to present new proposals for resolving the conflict to the UN Security Council later this month.