Syrian forces have resumed the bombardment of the city of Homs after the Arab League pledged its firm support for the opposition battling President Bashar al-Assad.
Opposition campaigners said tank fire was concentrated on two large Sunni Muslim neighbourhoods that have been at the forefront of opposition to President Assad.
"Mortar rounds and bombardment from BTRs (infantry fighting vehicles) are heavily hitting Baba Amro,” activist Mohammad al-Hassan told Reuters from Homs.
“We do not have numbers for any casualties because there is no communication with the district and the live feed camera relaying live footage from there appears to have been knocked out," he added.
The authorities say they are fighting "terrorists" in Homs.
The official news agency said a "terrorist group" had abducted an army colonel in the Qarabees neighbourhood of Homs, without giving a date.
At a meeting in Cairo yesterday, Arab League foreign ministers pledged for the first time to aid the opposition battling to overthrow President Assad.
Their resolution called for "opening communication channels with the Syrian opposition and providing all forms of political and material support to it".
The League also called on the UN Security Council to authorise a peacekeeping mission to Syria.
Syria has called the League's resolution "a flagrant departure from the group's charter and a hostile act that targets Syria's security and stability".
Any peacekeeping mission would require consensus from foreign powers, who have been divided on how to resolve a conflict that is descending into a civil war.
Russia and China have so far used their veto power to block action by the UN Security Council, most recently on 4 February.
According to the UN, more than 5,000 people have died since the uprising began.