We don't negotiate and we don't pay ransoms

Maxwell Gaylard UNDP

The motive for the kidnap is not known, but the head of the UNDP in Somalia, Maxwell Gaylard, said all efforts to arrange for Mr Abukar's release had been unsuccessful.

Since Somalia descended into clan warfare following the overthrow of Mohamed Siad Barre in 1991, abductions have been used by gunmen to extract ransom money.

Mr Gaylard told the BBC's Focus on Africa that a programme to eradicate polio would be one of those hit by the decision, which, he said "had not been taken lightly".

Mr Abukar suffers from high blood pressure and Mr Gaylard said he did not think that he had his medication with him.

Dangerous

Mr Abukar is the second UN official kidnapped by gunmen in Mogadishu this year.

In February, a Somali representative of the UN children's Fund, Unicef, was picked up by unidentified gunmen and released later.

Militiamen are everywhere in Mogadishu

The family said it paid no ransom, but AFP news agency quotes unnamed militia sources as saying money had changed hands before his release.

"We don't negotiate and we don't pay ransoms," said Mr Gaylard.

In a report published three months ago, UN Secretary general Kofi Annan said Somalia remained one of the most dangerous environments in which the UN operates, and that the security situation did not allow for a long-term presence.

The report was based on the findings of a security mission which went to Somalia in January, about 18 months after the fledgling interim government was set up.

In September 2001, the UN withdrew its international staff from Mogadishu because insurance companies refuse to insure flights in the wake of the attacks on the United States earlier that month.