Heavy fighting erupted in and around Damascus on Wednesday as rebels battled President Bashar Assad's forces, breaking a lull in the conflict, opposition activists and Syrian state media said.
Assad's forces also came under attack in the east of the country, where a suicide car bomb struck a military intelligence compound in the city of Palmyra, causing dozens of casualties, they said.
Authorities in Damascus closed the main Abbasid Square and the Fares al-Khoury thoroughfare as fighters attacked roadblocks and fortifications with rocket-propelled grenades and mortars.
Accounts of intense fighting were reported by a number of news agencies, including Al Arabiya News and The Associated Press, in addition to state and activist media.
"The areas of Jobar, Zamalka, al-Zablatani and parts of Qaboun and the ring road have become a battleground," activist Fida Mohammad said from the district of Qaboun.
Another activist said an army tank stationed at the main al-Kabbas roadblock on the ring road had been destroyed. Residents reported explosions across the east and north of the capital.
In Jobar, a working-class Sunni Muslim area adjacent to Abbasid Square, mosque speakers chanted "God is Greatest" in support of opposition fighters who attacked roadblocks in the neighborhood, activists said.
They said tanks stationed on the edge of the central district of Midan, just outside the walls of Old Damascus, shelled southern districts of the city.
Syrian state television said: "Our noble army is continuing its operations against the terrorists in Irbeen, Zamalka and Harasta and Sbeineg, destroying the criminal lairs."
Assad's symbols of power came under attack in Palmyra, 140 miles northeast of Damascus, on the main road to the oil-producing east of the country.
A bomb destroyed part of the back wall of the military intelligence compound near the Roman-era ruins in the city and then a suicide car bomber drove through, detonating the vehicle and destroying parts of the facility, activists in Palmyra said.
They said it was not immediately clear how many people had been killed in the blast and clashes which followed. Video footage, which could not be immediately verified, showed a large cloud of thick smoke rising in the city.
"The first car bomb struck at around six in the morning. The second one, which caused the larger explosion, broke through into the compound 10 minutes later," activist Abu al-Hassan said from the city.
He said tanks stationed in the compound fired shells in response into an adjacent residential neighborhood, killing several civilians.
Roadblocks across the city also came under attack.
The state news agency said two "suicide terrorists" blew up cars packed with explosives near a garage in a residential district, killing and wounding several people. Among those killed was a woman, it said.
Street demonstrations against Assad's rule erupted in Palmyra at the beginning of the revolt almost two years ago. But the army has since tightened control of the city, which is situated near a major oil pipeline junction.
After a failed uprising in the 1980s led by the Muslim Brotherhood against the rule of Assad's father, the late President Hafez Assad, thousands of rebels were executed in a military jail in Palmyra.