At least 25 people have been killed by explosions outside security forces compounds in Syria's second city of Aleppo, state media report.
State television said the death toll included both civilians and members of the security forces and blamed "armed terrorist gangs" for the blasts.
A spokesman for the rebel Free Syrian Army told the BBC it was behind them.
Residents of the city of Homs meanwhile say tanks are massed outside several opposition-held districts.
Overnight, tanks entered the eastern district of Inshaat, next to the protest centre of Baba Amr, the Syrian Observatory for Human Rights said.
There was also sporadic shelling throughout the city during the morning.
Activists say the intense bombardment of many parts of Homs by security forces since Saturday has left more than 400 people dead. US President Barack Obama has condemned the "outrageous bloodshed".
The opposition has called for nationwide protests on Friday to denounce Russia's veto of a UN Security Council resolution calling on President Bashar al-Assad's government to stop killing its own people.
But Russia's Deputy Foreign Minister Sergei Ryabkov said the opposition "bore full responsibility" because it had refused to begin talks with the government and accused Western powers of being "accomplices".
bbc.com
