Syrian forces resumed their bombardment of the city of Homs on Monday after Arab countries called for UN peacekeepers and pledged their firm support for the opposition battling President Bashar al-Assad.
Opposition campaigners said tank fire was concentrated on two large neighbourhoods that have been at the forefront of opposition to Assad. They said 23 people were killed on Sunday after a lull in shelling the previous day.
The government's assault on Homs has spurred Arab countries to ostracise Assad and promise tougher action. At a meeting in Cairo on Sunday, Arab League foreign ministers pledged for the first time to aid the opposition battling to overthrow Assad.
The League also called on the UN Security Council to authorise a peacekeeping force, a challenge to Russia and China which have so far used their veto power to block action by the world body, most recently on Feb 4.
In Homs, government troops concentrated their fire on Baba Amro neighbourhood in the south of the city and al-Waer in the West, which borders the Military College, a main assembly point for tanks and government troops, opposition campaigners said.
"Tank shelling has been non-stop on Baba Amro amd the bombardment on al-Wear began overnight," activist Mohammad al-Hassan said by phone.
He said al-Waer, scene of large pro-democracy demonstrations for months, had come under attack in the last several days from pro-Assad militia known as shabbiha.
"We heard that the Free Syrian Army has started responding by attacking roadblocks being manned by shabbiha. Communications with al-Waer have been cut off and the sound of shelling can be now heard," Hassan said.
The Free Syrian Army, led by defectors, has taken the main role in armed opposition to Assad's government. Accounts on the ground are difficult to verify because Syria restricts access by journalists.
The resolution approved by Arab League ministers in Cairo called for "opening communication channels with the Syrian opposition and providing all forms of political and material support to it", a remarkable statement from a body once known for keeping out of the internal affairs of its members.
The Arab League has turned decisively against Assad, led by Saudi Arabia and other Sunni-ruled Gulf monarchies who have long resented Assad's close ties to Shi'ite regional rival Iran.
The resolution did not spell out whether its proposed joint UN-Arab peacekeeping force would involve armed troops, or whether the aid offered to the opposition would include weapons.
If so, it would be the second time in less than a year the Arab League had called for outside intervention in an Arab state. Its decision to back a no-fly zone in Libya last March led to Western bombing that helped bring down Muammar Gaddafi.
Syria's uprising, in which the United Nations says more than 5,000 people have died, has become one of the bloodiest of the Arab Spring revolts sweeping the region since the end of 2010.
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.
Moscow and Beijing drew strong criticism from the West after they prevented the Security Council on Feb. 4 from backing an Arab plan that called for Assad to give up his powers. However, Western powers so far have shown no appetite for military action, despite their condemnation of the repression of the uprising.
Syria called the League's resolution "a flagrant departure from the group's charter and a hostile act that targets Syria's security and stability". Assad's government says it is fighting an insurgency by militants funded from abroad, and Arab states have turned against it as part of a regional power grab.
At the United Nations, U.N. Secretary-General Ban Ki-moon's spokesperson said the U.N. chief supported the "efforts of the League of Arab States to stop the violence in Syria and to seek a peaceful resolution of the crisis that meets the democratic and legitimate aspirations of the Syrian people".
"Action on the specific requests of the League will be a matter for the Security Council to consider, and he will remain in close contact with Member States as they take up these requests," Ban's spokesperson said in the statement.
Earlier on Sunday, Tunisia said it would host the first meeting on Feb. 24 of a "Friends of Syria" contact group made up of Arab and other states and backed by the West. A similar Libya contact group played a vital role in coordinating Western and Arab aid to that country's rebels last year.
"The Syrian people deserve freedom as much as their brothers in Tunisia, Egypt, Libya and other Arab states that witnessed major political change," Tunisian Foreign Minister Rafik Ben Abdessalem told the ministers in Cairo.
On Sunday armour-backed troops raided the al-Inshaat district of Homs, which has seen several incursions by loyalist troops over the past week. Tanks ran over civilian cars and troops ransacked houses and burned furniture in the streets as collective punishment, a statement by the Coalition of Free Homs said.
"The regime wants to punish the civilian population for supporting the Free Syrian Army," the statement said.
A Syrian Red Crescent aid convoy had reached Homs and volunteers were distributing food, medical supplies, and blankets to thousands of people affected by the violence, the International Committee of the Red Cross said in a statement.
"The population, particularly the wounded and sick, are bearing the brunt of the violence," the ICRC chief in Damascus, Marianne Gasser, said.
Activists said Red Crescent aid teams had been to districts populated by members of Assad's Alawite sect but had not reached Sunni neighbourhoods that bore the brunt of shelling.
A YouTube video showed a doctor in the Sunni al-Bayada district with the bodies of three men on the floor, the body of a woman on a table and an injured man on a bed, with no signs of any medical equipment except for an oxygen bottle.
"We do not have any medicine, equipment or staff. The hospital is this four metre (yard) by four metre room," the doctor said.
"The Red Crescent does not come here because the (army) shells it when it tries. Most of cases we receive are dying form bleeding because we don't have any blood units."
A lull in the bombardment earlier in the day prompted anti-Asssd rallies in Qusour, Bayada and Khalidua and Bab Houd districts of Homs. Demonstrations also broke out in Houla in the nearby countryside, which has also been under bombardment.
YouTube footage showed hundreds of youths holding shoulders and dancing under white-and-green Syrian flags from the time before Assad's Baath Party took power in a 1963 coup.
"Dignified Homs is dying. The world sold it by its silence, Mothers are suffering, but our dear God does not forget anyone," an activist sings as a crowd dances in front of him.
In the city of Hama, 50 km (28 miles) north of Homs, loyalist forces backed by tanks and armoured vehicles raided neighbourhoods on Sunday near the countryside where the Free Syrian Army has been active.
"It is the third day of such incursions. They fire heavy machineguns and anti-aircraft guns at random the, then they go in and raid houses and arrest dozens of people. The objective is to separate Hama from the countryside," activist Fady al-Jaber said from Hama.
He said tank fire killed three people on the edge of the city on Saturday and that families had started to flee the area.
Crowds on Sunday attended the funerals of some of 28 people.