Activists in Syria say scores of people have been killed in Homs, as government forces reportedly shelled the city for a sixth day.
The Local Co-ordination Committees, an umbrella opposition group, reported the deaths of 110 people in Homs on Thursday, but said it could not document the names of the victims due to heavy shelling.
"They targeted my neighbour’s house with rockets. I saw it with my own eyes," Omar Shakir, a resident of Bab Amr, a stronghold of the armed opposition, told Al Jazeera.
"This is the sixth day in a row we are being shelled by rockets, by mortars, by every weapon."
Shakir said residents of the neighbourhood were seeking safety on the ground floor of buildings as there were no underground shelters.
'Field hospitals hit'
During lulls in the shelling of Homs, loudspeakers were used to call for blood donations and medical supplies, residents said.
"There is medicine in the pharmacies, but getting it to the field clinics is very difficult, they can't get the medicine to the wounded," Mohammed Saleh, a Syria-based activist, told the Associated Press news agency by telephone.
Al Jazeera's Jane Ferguson reports from Homs, where some in the Alawite minority have joined the uprising
Human Rights Watch, the New York-based organisation, said in a report on Thursday that makeshift hospitals in besieged opposition areas of Homs were overflowing with dead and wounded people from government bombardments and snipers.
Medical supplies are running out and at least three field hospitals have been hi,t and people are bleeding to death as it is too dangerous for rescuers to bring them to safety, HRW said.
The rights watchdog said since the military operation against opposition neighbourhoods was launched on Friday night, government forces had fired hundreds of shells and mortar bombs, killing more than 300 people and wounding hundreds more, including women and children.
Elsewhere in Syria, an ambush by opposition fighters near the southern town of Deraa killed at least seven security forces and wounded dozens on Thursday, according to the Syrian Observatory for Human Rights.
"The security forces were travelling on board two buses when they were ambushed on a bridge by dissident soldiers," Rami Abdulrahman, head of the UK-based group, told the AFP news agency.
'Friends of Syria' meeting
The reports of violence came as the US said it was working with its European and Arab allies to organise the inaugural meeting of the Friends of Syria group to explore ways to further isolate President Bashar al-Assad and support his foes.
The state department said on Thursday that its chief Middle East envoy had been dispatched to Morocco, France and Bahrain to help put the meeting together, determine the group's membership and mandate. The Arab League was expected to announce the meeting as early as this weekend.
In-depth coverage of escalating violence across Syria
Morocco sponsored the UN Security Council resolution calling for Assad to step down that Russia and China vetoed. France, along with Turkey, has offered to host the Friends of Syria meeting.
In Moscow, Alexander Lukashevich, a Russian foreign ministry spokesman, reiterated the Kremlin view that though the bloodshed was regrettable, a solution was a matter for Syria.
"There is an internal conflict, the word revolution is not being used - it is a not a revolutionary situation, believe me," he said.
Earlier, Ban Ki-moon, the UN secretary-general, said that the head of the Arab League intended to send observers back into Syria and had raised the possibility of a joint mission with the UN.
"In the coming days we will further consult with the council before fleshing out details," he said on Wednesday.
"We stand ready to assist in any way that will contribute toward improvement on the ground.
"I fear that the appalling brutality we are witnessing in Homs, with heavy weapons firing into civilian neighbourhoods, is a grim harbinger of worse to come."
The Arab League suspended its observer mission to Syria last month, citing security concerns as the reason.