An aid convoy bringing supplies into the besieged district of the central Syrian city of Homs became trapped for several hours after coming under fire.
The Syrian Red Crescent said it had been "a challenge" to get its staff and the UN team out of the area.
The organisation's Khaled Erksoussi said the convoy came under attack from mortars and gunfire as it was leaving.
The firing came on the second day of a three-day ceasefire to allow aid in to the old city quarter.
Mr Erksoussi said UN officials are now meeting the Syrian government to discuss whether it is safe to continue with the operation on Sunday.
The government and opposition are trading accusations about who is responsible for breaking the ceasefire, the BBC's Jim Muir reports from neighbouring Lebanon.
Relief officials had earlier said the plan to send supplies into the embattled area was extremely sensitive, given the reluctance by some on the government side to see supplies going into rebel-held areas.
Seven Red Crescent workers and a similar-sized UN team were "pinned down" in the old city area of Homs for several hours in the dark.
One of the drivers was injured when mortars landed close to their convoy and shots were fired at their trucks.
Mr Erksoussi said the group had taken refuge in "buildings and safe areas" until they were able to get out, shortly before 22:00 local time (20:00 GMT). They had to leave two of their damaged trucks behind.
"Although the team was shelled and fired upon we managed to deliver 250 food parcels, 190 hygiene kits and chronic diseases medicines," the Syrian Red Crescent said on Twitter.
The Red Crescent, in a joint operation with the UN, is trying to deliver food, water and medicine by truck to some 3,000 civilians in rebel-held areas.
On Friday, the first day of the agreed three-day ceasefire, more than 80 children, women and elderly people were evacuated.
Many of those evacuated on Friday looked frail and described extreme hardships inside the area, which has been under army siege for nearly a year-and-a-half.
They said bread had not been available for months, and many residents were gathering weeds and leaves to eat.
Vulnerable civilians such as children, old people and medical cases were brought out of the besieged area, sometimes carried by Red Crescent volunteers.
They told journalists that there were more people trapped in the city who had wanted to leave.
Homs has been a key battleground in the uprising against Syrian President Bashar al-Assad.
The army launched a series of big attacks to recapture rebel areas in the Old City in the beginning of 2012, with almost daily bombardments.
Thousands have been killed, large areas have been reduced to rubble and many neighbourhoods lie in ruins.
The situation in besieged districts of the city since June 2012 was discussed during peace talks in Geneva a week ago, but the humanitarian aid deal was actually struck between the governor of Homs and the UN resident co-ordinator in Syria.
The Syrian government is making no connection between the Homs agreement and the peace talks, but it was first mooted by the mediator there, Lakhdar Brahimi, our correspondent says.
Another round of talks is scheduled to begin on Monday and the Syrian government has confirmed it will attend.