The Red Cross delivered aid to areas around the battered Baba Amro district of the Syrian city of Homs on Sunday, but was blocked from entering the former rebel stronghold itself, three days after anti-government fighters fled a month-long siege.
In a further indication civilians were being caught up in the conflict, up to 2,000 Syrians fled into neighbouring Lebanon, the U.N. Refugee Agency said.
The International Committee of the Red Cross (ICRC) said it had been prevented from entering Baba Amro by Syrian ground forces despite receiving government permission, a move activists said was to prevent aid workers witnessing army massacres.
We have the green light, we hope to enter, we hope today is the day, said the ICRC's Damascus-based spokesman Saleh Dabbakeh, declining to give further details about what he said were sensitive talks with Syrian officials.
We are very concerned about the people in Baba Amro.
After a month of bombardment by President Bashar al-Assad's forces, concerns mounted for freezing, hungry and wounded civilians in Homs, which on Saturday had come under renewed shelling by government troops, anti-Assad activists said.
U.N. Secretary-General Ban Ki-moon said on Friday he had received grisly reports troops were executing and torturing people in Homs after insurgents abandoned their positions.
Aid workers began delivering supplies to areas near Baba Amro where people had fled, the ICRC said.
It is a positive step. But we want to enter Baba Amro today, ICRC spokesman Hicham Hassan told Reuters in Geneva.
South of Homs, the border town of Qusair came under shelling by government troops, forcing residents to flee on foot to neighbouring Lebanon, a Reuters witness said.
The people said they were sat at home and suddenly the shelling started and they fled. They said it was tank shelling and gunfire, said Reuters reporter Afif Diab.
He spoke at the border to what he said were mainly women fleeing with their children. Blasts could be heard from the Lebanese border, which is some 12 km (7 miles) from Qusair.
Other Lebanese border sources spoke of attacks in Syria by aircraft, but reports could not immediately be verified.
Between 1,000 and 2,000 (Syrians) are in the process of coming from Syria to Lebanon, the UNHCR's deputy representative in Lebanon, Jean-Paul Cavalieri, told Reuters.
The outside world has proved powerless to halt the killing in Syria, where repression of initially peaceful protests against Assad's rule sparked an insurrection by army deserters and others.
The government says it is fighting foreign-backed terrorists it blames for killing hundreds of soldiers and police across the country.
Activists reported government raids in Hama in which one young man was shot dead, and heavy shelling in the town of Rastan, north of Homs, where rebels have been hiding.
Residents told me that shelling started early this morning shortly after helicopters and spotter planes were seen above the town, said Rami Abdelrahman, head of the Britain-based Syrian Observatory for Human Rights.
Clashes between Free Syrian Army defectors and Syrian troops were reported in Jebel al-Zawiya in Syria's north, and activists said government forces had used tear gas to disperse an anti-Assad protest in the northern city of Aleppo.
Abdelrahamn also reported an attack on a Syrian army weapons depot by rebels near Homs on Saturday, killing and wounding up to 50 Syrian troops. Activists' reports are difficult to verify independently due to Syrian reporting restrictions.
The United Nations says Syrian security forces have killed more than 7,500 civilians since the revolt against the Assad family's four-decade rule began in March last year.
The Syrian government said in December that armed terrorists had killed more than 2,000 soldiers and police during the unrest.
Lebanon deployed more troops to its northern border in response to the violence in Syrian towns nearby, a Reuters witness said, part of a conflict that risks dragging in regional powers with rival sectarian interests.
In the Lebanese capital Beirut, hundreds of soldiers and scores of military trucks and jeeps blocked off the city centre on Sunday during protests for and against Assad, whose ruling clan are Alawites, an offshoot of Shi'ite Islam.
Lebanon is mainly made up of Shi'ites, Sunnis and Christians, and is home to the powerful Shi'ite militant group Hezbollah, which is backed by Shi'ite Iran.
Sunni Arab states Qatar and Saudi Arabia have been among the loudest calling for Assad's downfall, and have even suggested arming his opponents.
We sacrifice our blood and souls for you Bashar, chanted a pro-Assad crowd of some 500 people. Some stepped on photos of Saudi Arabia's King Abdullah and threw shoes at a poster of him.
A similar sized anti-Assad crowd sang: We sacrifice our blood and souls for you, Homs.
Former Syrian ally Turkey said Assad was guilty of war crimes while China said it was deeply worrying that the situation in Syria remains grave.
China, which along with Russia has twice vetoed U.N. Security Council resolutions condemning Damascus, urged government and rebels to end the violence and start talks, but reiterated its opposition to foreign military intervention.
We oppose anyone interfering in Syria's internal affairs under the pretext of 'humanitarian' issues, said a foreign ministry statement carried by Xinhua news agency.
Russian Foreign Minister Sergei Lavrov will join Arab counterparts at a meeting in Cairo this month to discuss the Syrian crisis, the Arab League said on Sunday, a move that could indicate Moscow is shifting its stance on the issue.
(Additional reporting by Stephanie Nebehay in Geneva and Ayman Samir in Cairo; Writing by Mohammed Abbas; Editing by Robin Pomeroy)