Al Qaeda's North African wing threatened on Sunday to kill a British hostage if Britain did not release a Jordanian Islamist it was holding.
"We demand that Britain release Sheikh Abu Qatada, who is unjustly (held), for the release of its British citizen. We give it 20 days as of the issuance of this statement," al Qaeda in the Islamic Maghreb said in a posting on an Islamist website.
"When this period expires the mujahideen will kill the British hostage," said the group, adding that it still held a Swiss national "until we have achieved our legitimate demands" but gave no more details.
The British foreign office called for the immediate and unconditional release of the hostages.
"We can confirm that we are aware of the report in question and it is being analysed," a Foreign Office spokesman said in a statement.
"Hostage-taking can never be justified, no matter what the cause. We call on all those holding hostages to release them immediately and unconditionally."
Analysts say the Sahara desert in West Africa has become increasingly insecure and the lines between ideology and criminality have become blurred.
Tuareg rebellions are simmering in both Mali and Niger, Islamist groups are seeking to spread their influence south from Algeria and there is a long tradition of trafficking in cigarettes, weapons and people.
Abu Qatada, named by a Spanish judge as the right hand man in Europe of Osama bin Laden's al Qaeda network, has been held in Britain since 2005. He denies belonging to the group.
Britain's highest court ruled in February he could be deported to Jordan despite fears he may be tortured there.
Two Canadian diplomats and two European tourists held by the group have already been released, Mali said this week.
Robert Fowler, a United Nations envoy to Niger, disappeared with his aide last December while two Swiss, a German and a Briton were kidnapped on the Mali-Niger border in January.
Earlier this month, a Malian security source said a team of mediators was negotiating the release of the European tourists.
A Malian security source told Reuters the hostages had been handed to local authorities in Gao, over 625 miles (1,000 km) northeast of Bamako.