A convoy delivering aid to civilians trapped in Syria's Homs was fired on Saturday and a number of people killed or wounded, raising questions about whether the hard-won humanitarian mission can proceed.
The violence, which the regime and rebels blamed on each other, came after 83 children, women and elderly people who survived more than 600 days of a choking army siege were evacuated in a UN-supervised operation on Friday.
The mission was made possible by a surprise UN-brokered deal between the government and rebels to observe a three-day "humanitarian pause" in hostilities.
It was unclear if the violence will stop the hard-won deal for the United Nations to deliver much-needed aid to civilians in Homs and resume operations to evacuate those who wish to leave.
The clashes erupted in the morning in rebel-held areas of the Old City of Homs.
Hours later a Syrian Red Crescent convoy came under mortar attack and gunfire.
"Shots fired targeting aid trucks and the team," the Red Crescent said on Twitter.
"Mortar shells falling in close proximity near the team and aid trucks that moved into Old City," it added, saying a driver was wounded.
State news agency SANA said four Red Crescent volunteers were wounded by "armed terrorist groups," as the convoy was entering the Old City.
Homs Governor Talal al-Barazi said two aid vehicles entered the Old City but "terrorist groups prevented the entrance of other vehicles by firing mortar rounds on the road."
The regime labels as terrorists rebels fighting to topple President Bashar al-Assad in a nearly three-year war that has killed more than 136,000 people.
The Syrian Observatory for Human Rights reported that two Homs residents were killed in the shelling and several wounded, including a media activist.
Activists, meanwhile, said that several aid workers were still inside besieged areas of Homs after sunset, including UN Resident Coordinator Yaacub El Hillo.
And the Syrian Arab Red Crescent posted a statement on Facebook saying "all SARC Homs volunteers in the Old City are in good health, all other news is not true."
Regime, rebels trade accusations
Five explosions were heard at 8:30 am (0530 GMT) in the besieged neighbourhoods, the Britain-based Observatory said.
Barazi said "terrorist groups broke the truce this morning in the Old City... by launching mortar rounds at the police headquarters in the Saa area."
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But activists said the regime was responsible.
"The besieged areas have been pounded with mortar rounds since Saturday morning," said the Unified Media Office in the besieged areas, adding that the road to be used by aid convoys was hit.
The exiled opposition expressed concern the aid delivery could be aborted, saying it would be "devastating" for besieged civilians.
Desperately needed food and medicines have been held up for months in a UN warehouse in a government-controlled area.
The UN says trucks are carrying emergency rations for 2,500 people, medical kits and bedding, as well as cash and other support for the "immediate needs both of those who choose to be evacuated from the area and of those who remain inside" after Friday's evacuations.
Activists say those trapped have been surviving for months on little but olives and wild cereals.
UN humanitarian chief Valerie Amos hailed the truce and said there were plans for more evacuations and aid deliveries in the next few days.
And a cleric in the rebel enclave, Abdul Hareth al-Khalidi, told AFP a second operation to evacuate civilians would take place on Sunday.
Homs, much of which has been reduced to rubble, was dubbed "the capital of the revolution" by activists before a bloody 2012 counter-offensive by regime forces recaptured much of the city.
The army blockaded the remaining rebel-held areas after their 2012 assault. They tightened the noose last summer by capturing the town of Qusayr, which cut off rebel supply lines to neighbouring Lebanon.
Barrel bombs rain on Aleppo
In other violence Saturday at least 20 people were killed when regime helicopters dropped barrel bombs on the northern city of Aleppo, where the army is pressing an advance to recapture rebel-held areas.
The Observatory which reported the bloodshed, also said that barrel bombs were dropped on Daraya, a rebel basion southwest of Damascus, while 16 people were killed in unrest in the southern province of Daraa.
The raids came as Al-Qaeda affiliate Al-Nusra Front and allied Islamist rebel groups launched a new offensive against the jihadist Islamic State of Iraq and the Levant in Syria's oil-rich east.
Saturday's clashes come a day after ISIL took over several rebel bases in Hasakeh province, north of Deir Ezzor, across the border from Iraq.
Deir Ezzor is a key conduit for ISIL to send weapons and fighters from Iraq into Syria.