Opposition activists say more than 300 people have been killed during fighting across Syria, making it the bloodiest day since the uprising against President Bashar al-Assad began in March last year.
Fighting is continuing in the capital, Damascus, and opposition fighters have seized control of some of Syria's border crossings with Iraq and Turkey.
Rebels have torched the main police headquarters in the heart of old Damascus.
Reuters reports the battle for parts of the capital raged into the early hours of the morning, with corpses piled in the streets.
The regime's troops are using helicopter gunships and tanks to reclaim opposition-held parts of the city but in some neighbourhoods, residents say there are signs the government's presence is diminishing.
Meanwhile, Syrian state television says security chief Hisham Ikhtiar has died of wounds suffered in the bombing two days ago that killed three of Mr Assad's top security officials, the fourth high-ranking fatality.
All Iraqi crossings taken - Iraq
Iraq's deputy interior minister says the Free Syrian Army has taken control of all of Syria's crossings with Iraq.
Reuters reports Iraqi officials have confirmed the rebels are now in control of the Syrian side of the main Abu Kamal border checkpoint on the Euphrates River highway, one of the major trade routes across the Middle East.
Iraqi officials say at one remote border outpost rebels killed more than 20 Syrian soldiers.
The major crossing with Turkey, at Bab al-Hawa, was also captured but the rebels may have since pulled out.