Jean Fabre of the U.N. Development Program said it was still unknown who died or which U.N. agencies they represented. Fabre said he received the information from Marc Destanne De Bernis, the agency's top official in the Algerian capital.
The explosion occurred around 9:30 a.m. (0830 GMT) and blew off the front of the U.N. refugee agency building, UNHCR chief spokesman Ron Redmond said.
It apparently caused even worse damage to the main U.N. building housing the U.N. Development Program and other agencies diagonally across the street.
The attack recalled the Aug. 19, 2003, attack on U.N. headquarters in Baghdad with a truck bomb that killed top U.N. envoy Sergio Vieira de Mello, and 21 others.