United Nations humanitarian chief Valerie Amos says she has grave concerns for people missing from the Syrian city of Homs.
Baroness Amos, who visited Homs a day ago, says the bombed-out Baba Amr district felt like it had been closed down.
The Red Cross says Syrian Red Crescent workers finally allowed into Baba Amr have found most of its residents gone.
It says most of them appear to have fled to other areas of the city or to a nearby village already visited by Red Cross and Red Crescent workers, the BBC reports.
Meanwhile, activists say dozens of people have been killed in the Jobar district of Homs in a new massacre they describe as reprisal killings.
The BBC quotes the Local Co-Ordination Committees as saying 44 of those killed came from just a handful of families.
The group says 20 of the dead belonged to a single family, and 16 to another.
The claims cannot be verified as international media inside Syria are heavily restricted but the BBC's correspondent in neighbouring Lebanon says activist groups continue to report the summary execution of men from Baba Amr, the butchering of entire families, and the systematic mass rape of women.
He says opposition groups are urging Baroness Amos to go back and delve deeper.