Syrian forces on Wednesday blasted the rebel-held Khaldiyeh district of Homs city with rockets and shells for a second straight day, raising fears of a "repeat of Baba Amr," activists said.
The assault came as UN chief Ban Ki-moon, on a visit to Jakarta, said the Syrian crisis had "massive" regional repercussions, and the priority must be to stop the violence and give urgent access to humanitarian aid.
"Khaldiyeh is being bombed, with shells and rockets, for a second day," Hadi Abdullah of the Syrian Revolution General Commission told AFP, reached by telephone from Beirut.
The Syrian Observatory for Human Rights, a Britain-based monitoring group, said 14 civilians were killed in Khaldiyeh on Tuesday and also reported renewed clashes in the Damascus area.
Abdullah said he feared a repeat of the month-long battering that killed hundreds in Homs' Baba Amr district before the army moved in on 1 March following a withdrawal by Free Syrian Army rebels.
"That would be a catastrophe," he said.
Abdullah said thousands of residents who fled Baba Amr and from other parts of the city in central Syria had taken refuge in Khaldiyeh, "the last front left" in Homs.
The UN Security Council, meanwhile, aimed to close ranks on a diluted statement to bolster UN-Arab League envoy Kofi Annan's mission to end the year-old crisis in Syria, after Russia refused to back any "ultimatum."
Annan, who held talks in Damascus on 10 and 11 March, briefed the Security Council on Friday.
UN Secretary-General Ban said in a speech to a defence conference in the Indonesian capital that Annan was "working tirelessly."
The prepared text of Ban's speech released to media in Jakarta said Annan was expected to return soon to Damascus. This line was removed from the speech as delivered, and Ban did not give any timeframe for when Annan might return.
Martin Nesirky, a spokesman for Ban, told AFP: "The joint special envoy's technical team is still in Damascus, and he is still waiting to hear more details from them before he decides on his travel plans."
Ban told his Jakarta audience that the UN had three major priorities in Syria.
These were "an immediate end to the violence – all violence," an "inclusive political dialogue" to shape the country's future, "and thirdly we have to provide, immediately and urgently, humanitarian access."
"We all have a responsibility to work for a resolution of this profound and extremely dangerous situation and crisis," Ban said. The situation was "a crisis that has potentially massive repercussions for the region of the world."
Russia said on Tuesday it was ready to back either a Security Council statement or resolution on Annan's proposals on ending the crisis as long as it contained no ultimatums.
At the United Nations, diplomats from the 15-nation Security Council held four hours of talks on Tuesday on the Western-drafted presidential statement.
Russia led resistance to part of the statement that said the council would "consider further measures" if President Bashar Al-Assad does not act upon Annan's peace plan, diplomats said.
Russia and China have already vetoed two full resolutions on Syria.
The latest proposed statement, obtained by AFP, does not condemn the violence but would express "gravest concern" at the deteriorating crisis in Syria and "profound regret" at the thousands of dead.
Diplomats in New York said the statement, which carries less weight than a full resolution, could now be adopted on Wednesday.
On the ground, fierce clashes broke out in the Damascus suburb of Harasta overnight between rebels and security forces near an air force intelligence post, the Observatory said.
It reported heavy machinegun fire, without giving any casualty toll. A "tense" calm had returned to the area on Wednesday morning.
A security clampdown has been ordered in the capital followed what activists said was a hit-and-run attack in the heavily guarded Mazzeh neighbourhood on Monday that killed at least three rebels and a member of the security forces.
It also came on the heels of deadly twin suicide car bombings targeting security buildings in Damascus on Saturday.
An Islamist group claimed responsibility for the suicide car bombings in Damascus saying they were to avenge the Syrian regime's "massacre of Sunnis," in a statement posted online.
Al-Nusra Front to Protect the Levant said its militants carried out "a series of military operations... especially the air force security" buildings of the "criminal regime" in Damascus.
The attacks were "in response to the continued shelling by the regime of residential districts of Homs, Idlib, Hama and Daraa," it said, listing major centres of opposition across Syria.
AFP could not verify the authenticity of the statement or of reports from monitors as Syrian authorities restrict the movements of foreign media.
Syria's state news agency SANA said a number of security officials and civilians were killed in a suicide car bombing in the southern province of Daraa on Tuesday, without giving a specific casualty toll.
Syria has blamed the car bombings on "armed terrorist gangs" that it holds responsible for the bloodshed in the country. It has also pointed to an Al-Qaeda role in the violence.
Opposition activists have accused the Damascus regime of stage-managing attacks, such as the car bombings, to cause inter-sectarian strife.