Army reinforcements, including tanks, are heading towards the city of Homs, a Syria-based activist has claimed.
Syria-based activist Mustafa Osso said he does not think the regime will be able to retake Homs through military force as residents plan to fight until "the last person". He added that Homs is facing "savage shelling that does not differentiate between military or civilian targets".
Rami Abdul-Rahman, who heads British-based activist group the Syrian Observatory for Human Rights, said he expects the regime to try retake the Baba Amr district of Homs.
The Observatory said that the latest shelling of Baba Amr killed five civilians. In neighbouring Lebanon, security officials said at least three wounded Syrians were brought for treatment in the eastern town of Chtoura. The officials said the wounded came from the Baba Amr attacks.
Clashes between military rebels and Syrian forces are growing more frequent and the defectors have managed to take control of small pieces of territory in the north as well as parts of Homs province, which is Syria's largest stretching from the border with Lebanon in the west to Iraq and Jordan in the east. Increasingly, Syria appears to be heading towards an all-out civil war.
Assad's authoritarian regime may be trying to subdue Homs - an important stronghold for anti-Assad groups - before a planned referendum on Sunday on a new constitution. The charter would allow a bigger role for political opposition to challenge Assad's Baath Party, which has controlled Syria since a 1963 coup.
But the leaders of the uprising against Assad have dismissed the referendum as an attempt at superficial reforms that do nothing to crack the regime's hold on power. Assad still counts on support from Iran and allies such as Russia, which fears losing its main Arab partner. But his government is facing escalating pressure and isolation from Western and Arab states.
Mr Osso said the three convoys heading toward Homs comprise dozens of vehicles from the eastern suburbs of the capital Damascus, an area that was reclaimed by Assad troops from rebels late last month.
Meanwhile, the International Committee of the Red Cross has announced it is trying to broker a humanitarian ceasefire in Syria. ICRC spokeswoman Carla Haddad said the group is "discussing several possibilities with all those concerned and it includes a cessation of fighting in the most affected areas".
She said that the Geneva-based aid group has been in talks with Syrian authorities and opposition groups for some time but attempts to negotiate a ceasefire were "an important new step".