The International Committee of the Red Cross called on the warring parties on Thursday to let people leave the besieged Ukrainian city of Mariupol safely and to allow aid in.
Up to 40 ICRC staff and their families had to flee the port along with other civilians on Wednesday, because they had "no operational capacity any more," the organisation's head Peter Maurer told a news conference.
But the ICRC would be making arrangements to bring in aid as soon as it could safely, he added.
The ICRC was also still trying to get access to prisoners of war from both sides, he told journalists by video link from Kyiv. Captured troops should be treated with dignity and not exposed to "public curiosity," he added.
Rescue workers on Thursday dug survivors out of the rubble of a theatre in Mariupol which Ukraine said had been hit by a Russian air strike while people sheltered there from bombardments.
Russia denied striking the theatre. But its forces have blasted cities and killed many civilians in its assault on Ukraine, which it calls a "special operation".
Maurer told the Geneva press briefing he did not want to make any premature comments about what had happened at the theatre.
He said his neutral aid agency was ready to help evacuate civilians from the port city and deliver aid, but that Ukraine and Russia had to reach agreement on terms first.
"The most pressing issue is those which have been most widely publicised - it's access (to) and exit of besieged and combat zones in which the frontlines are close together and civilians trapped," Maurer said.
"Despite all the difficulties of negotiating access and evacuation routes, we've seen an increasing number of civilians able to leave in agreed upon and safe corridors. We are at the beginning of a process," he added on the second day of a five-day visit.
Asked about difficulties in Mariupol, he said: "Hold-ups are first and foremost the lack of trust between parties to the conflict, it's the military posture on the ground, it's roads which are contaminated, weapons contaminated, and therefore unsafe."
(Reporting by Stephanie Nebehey and John Revill; Editing by Alex Richardson and Andrew Heavens)
