Syria's Bashar al-Assad should go, says Arab League
The rebels told the BBC's Paul Wood, undercover near the Syrian capital, that the deaths of four top officials were a severe blow to the government.
Our correspondent says Islamist rebels where he is are receiving weapons and money from outside.
Fighting continued overnight.
Government forces recaptured parts of Damascus, the suburbs of Barzeh and Mezzeh, which had fallen into rebel hands.
There and in other quarters, activists said a number of suspected rebels or sympathisers were summarily executed.
Fighting was also reported in Syria's second city, Aleppo.
'Transitional government'
After an emergency meeting in Qatar, Arab League foreign ministers called on President Assad to resign rapidly, and offered his family safe passage out of Syria.
They also called on the Syrian opposition to form a transitional government.
However, the BBC's Jim Muir, in neighbouring Lebanon, says the call appears to have fallen on deaf ears.
Mr Assad held a meeting with his new army chief of staff and gave him instructions, reportedly including a drive to crush armed rebels.
Source: BBC