Robert Fowler became the UN special envoy to Niger in July last year
A man claiming to be from al-Qaeda in the Islamic Maghreb says the group is holding two Canadian diplomats and four European tourists kidnapped in Niger.
The audio recording of the man, who identified himself as Salah Abu Mohammed, was broadcast by Arabic satellite station al-Jazeera.
The two Canadians - the UN envoy to Niger, Robert Fowler, and his colleague - went missing in mid-December.
The Europeans were kidnapped along the border of Mali and Niger in January.
The Swiss couple, a German woman and a British man had just attended a Tuareg cultural festival in Mali.
The authenticity of the tape, in which the group said it would soon issue conditions for the hostages' release, has not been verified.
But Maghreb analyst Mohamed Ben-Madani says it seems to follow the group's usual tactics.
"It is their normal practice not to speak until they are sure that they have got good people for good money and they are in a safe place before any negotiations," he told the BBC's Focus on Africa programme.
The group usually demands large sums of money for the release of their captives, he said.
Al-Qaeda in the Islamic Maghreb emerged in early 2007 from the feared Algerian militant group, the Salafist Group for Preaching and Combat (GSPC), which aligned itself with Osama Bin Laden's international network.
Mr Ben-Madani said the group's influence is spreading and it now has small branches in places like Mali, Niger, Mauritania, Nigeria and Morocco.
"It is spreading and growing in numbers," he said.
He said money from kidnapping helped to finance their operations.