Kidnappers on Wednesday released a senior U.N. peace envoy and three other Western hostages, following months of captivity, a Malian official said.

Presidential spokesman Seydou Cissouma said Robert Fowler and his U.N. aide Louis Guay were set free along with two female tourists. Both men are Canadians.

Al Qaeda's North Africa branch had claimed it carried out the kidnapping, saying it was holding Fowler and the others after taking them captive in neighboring Niger.

The U.N. staffers were captured in December, while the two women were members of a group of four tourists seized a month later. Cissouma had no further details and there was no word on the fate of the two other missing tourists.

The Al Qaeda group did not issue demands for the hostages' release, but in the past it has obtained ransoms for Western tourists kidnapped in the Sahara, the world's largest desert.

Canadian Prime Minister Stephen Harper said both Canadians were safe and welcomed their release. He said the governments of Mali and Burkina Faso negotiated the release of the men, but wouldn't comment on whether they paid ransom or agreed to a prisoner exchange.

"What efforts or initiatives may have been undertaken by other governments are questions you'll have to put to those governments," Harper said.

U.N. Secretary-General Ban Ki-moon expressed appreciation to the authorities in Burkina Faso, Mali and Niger, U.N. deputy spokeswoman Marie Okabe said.

"He particularly appreciates the role that Canada has played in ensuring that Mr. Fowler and Mr. Guay would be released unharmed," Okabe said. "The secretary-general reiterates his belief that U.N. staff members carry out valuable work around the world, which they should be able to do without fear of harassment or intimidation."

Al Qaeda in Islamic North Africa, known by the French language acronym AQMI, is an Algeria-based group that joined Usama bin Laden's terrorist network in 2006 and conducts dozens of bombings or ambushes each month. It operates mainly in Algeria but is suspected of crossing the country's porous desert borders to spread violence in the rest of northwestern Africa.

President Mamadou Tandja of neighboring Niger has blamed Fowler's abduction on a rebel group from the northern Niger ethnic minority of Tuareg nomads who are battling the government.

Tuareg rebels from the Front For Forces of Redress retracted their initial statement claiming responsibility for the kidnapping, saying their Web site had been hacked. But some Western intelligence officials believe the Tuaregs may have traded the hostages to Al Qaeda in Islamic North Africa.