Regime aircraft hammered insurgent bastions nationwide on Sunday as rebels said they now control most of the country and have moved their command centre from Turkey to "liberated areas" inside Syria.
With deadly violence raging across Syria, UN-Arab League peace envoy Lakhdar Brahimi prepared to brief the UN Security Council on Monday about talks he had with both President Bashar al-Assad and the opposition.
Brahimi discussed Syria with UN chief Ban Ki-moon on Saturday and both agreed that the 18-month crisis was "a steadily increasing threat to regional peace and stability," a statement said.
On the ground, at least 40 people were killed on Sunday, the Syrian Observatory for Human Rights said, as Syrian aircraft carried out strikes on rebel bastions, especially in central Homs province, Deir Ezzor in the east and areas of Damascus.
Apartment blocks in Albu Kamal, a town in oil-rich Deir Ezzor province, were targeted as rebels and soldiers battled on the ground in several districts of the town on the Iraqi border.
"The insurgents are trying to wrest control of this strategic town" said Observatory chief Rami Abdel Rahman. Losing Albu Kamal would be "a deadly blow for the regime," he added.
Helicopter gunships opened fire on the Damascus neighbourhoods of Barzeh and Qaboon as well as the suburb of Harasta, while troops pounded rebel areas in Aleppo in the north and neighbouring Idlib and Daraa in the south, the Observatory reported.
A blast shook central Damascus near a five star hotel and the national museum, the watchdog said quoting witnesses who added that the explosion may have targeted a military vehicle.
The Britain-based group, which gathers information from a network of activists on the ground, said warplanes also raided Jebel al-Akrad in the coastal province of Latakia.
In Aleppo, rebels destroyed two fighter planes on the ground in Orm, a rebel commander told AFP.
Residents in the village of Bianoun north of Aleppo told AFP that aircraft also hit a rebel house where a meeting was underway, destroying it and killing everyone inside. The report could not be independently verified.
Security forces also carried out raids and arrested several civilians in the southern Damascus neighbourhood of Al-Hajar al-Aswad, the Observatory said.
As the fighting continued unabated, Colonel Ahmad Abdul Wahab of the Free Syrian Army said the regime's aerial superiority was the only thing preventing the FSA from taking control of the capital.
"We control most of the country. In most regions, the soldiers are prisoners of their barracks. They go out very little and we can move freely everywhere, except Damascus," Abdul Wahab told AFP.
"With or without outside help, the fall of the regime is a question of months, not years," he said.
"If we had anti-aircraft and anti-tank missiles, we could quickly gain the advantage. But if foreign countries don't give us these, we will still win. It will take longer, that's all."
-- Next step to 'liberate' Damascus --
Abdul Wahab, a colonel in the regular army only nine months ago, said his defection was driven by "the magnitude of the crimes of the regime, which is killing its own people."
He said he commands four katibas (battalions) which make up the "Nasser Salaheddin" brigade in Aleppo and the region.
Abdul Wahab said he attends daily meetings with FSA leaders in the northern metropolis, where orders are given to him and other battalion commanders.
On Saturday, the FSA said the next step would be to "liberate" Damascus as it announced that it has moved its command base from Turkey to areas it controls inside Syria.
"The Free Syrian Army command has moved into liberated areas of Syria following arrangements made with battalions and brigades to secure these zones," FSA chief Colonel Riyadh al-Asaad said in a video posted on the Internet.
Nearly 80 percent of towns and villages along the Turkish border are outside the control of Damascus, according to the Observatory.
Meanwhile, Assad's only sister, Bushra, whose husband was killed in a July bombing, is now living in Dubai with her children, Syrian residents of the Gulf emirates told AFP.
Bushra's husband General Assef Shawkat, an army deputy chief of staff, was killed along with three other high-ranking officials in a July 18 bombing at the National Security headquarters in Damascus.
Ayman Abdel Nour, editor-in-chief of opposition news website all4syria.com, said Bushra, a pharmacist with five children, left Syria after "differences" with the president.
And in Damascus, 20 government-tolerated opposition parties met on Sunday to discuss a solution to the crisis in the presence of the ambassadors of Russia and Iran, staunch allies of Assad's government.
Raja al-Nasser of the National Coordination Committee for Democratic Change called at the meeting for an end to the "barbaric bombing" to move toward a political process that would "put an end to the current regime".
According to the Observatory, at least 29,000 people have been killed since the revolt against Assad's rule erupted. The United Nations puts the toll at more than 20,000.