Fifteen foreigners are believed to have been kidnapped in a remote area of Ethiopia where separatist rebels operate.
Two groups - one of 10 French tourists, the other comprising a mixture of nationalities - disappeared earlier in the week while visiting the arid Afar region in the north-east of the vast Horn of Africa nation.
Afar separatists started a low-level rebellion against the government in the 1990s, calling for a separate Afar state on territory straddling Ethiopia, Eritrea and Djibouti.
The second missing group, thought to be touring the Danakil Impression - one of the lowest and hottest places on earth - included one Briton, one French national and one Italian, according to sources.
Nationalities of the other two were not immediately known and it was not known exactly where the first group had been.
In 1995, nine Italian tourists were captured by Afar tribesmen in the desert, then released two weeks later.