* Britain, Italy checking video for authenticity
* Video shows hostages saying kidnappers are al Qaeda
* Would be first known kidnap by al Qaeda links in Nigeria
* Security experts say hostages may have been sold (Adds Boko Haram attack, regional al Qaeda context)
By Joe Brock
ABUJA, Aug 4 (Reuters) - A video which appears to show a Briton and his Italian colleague who were kidnapped in May in northern Nigeria is being checked for authenticity by foreign ministries, after the hostages said they were being held by al Qaeda.
The one-minute video shows hostages blindfolded and on their knees, while three armed men stand behind them, their faces hidden by turbans, according to the AFP news agency, which was sent the video in Ivory Coast.
It was not clear when, or where the film was made and it could not be independently verified.
"We can confirm that two people, including a British national, were kidnapped in Nigeria on 12 May," a British Foreign Office statement said. "A video has been released allegedly showing the hostages and officials are urgently checking its authenticity."
The Italian foreign ministry also put a statement on its website saying it was evaluating the video.
Al Qaeda's north African wing, Al Qaeda in the Islamic Maghreb (AQIM), operates in neighbouring Niger and has kidnapped foreign workers there but this would be the first such incident in Nigeria.
Countries in Africa's Sahel-Sahara region have stepped up efforts to counter an increased threat from gunmen linked to al Qaeda, who frequently cooperate with and operate alongside rebels, bandits and traffickers in the largely desert zone.
If the kidnappers were linked to al Qaeda it would be a significant escalation in the security threat in Africa's most populous nation, scene of attacks in recent months by the radical Islamist sect Boko Haram.
Security experts and diplomats had believed the two men were seized by local criminals. They said it was not yet clear if the abductors were al Qaeda members but did not rule it out due to the dangers in the surrounding region.
NEW TERRITORY
"It is certainly feasible that the men have been sold to AQIM/al Qaeda, although they are not likely to have been the original kidnappers," one security expert based in Nigeria said.
A western diplomat told Reuters the abduction was escalated to "the highest level" by the British and Italian foreign ministries some weeks ago, an indication that they were aware of the seriousness of the kidnappers.
The two men were working for a construction company and were seized from their accommodation in the capital of Kebbi state, near Nigeria's northwestern borders with Niger and Benin.
"We are working to secure the hostages' safe and swift release. We ask those holding the two men to show compassion and release them, enabling them to rejoin their families," the British Foreign Office statement said.
Hundreds of oil workers have been kidnapped in Nigeria's oil-producing Niger Delta hundreds of kilometres away in the southeast, but such attacks are relatively rare in the north.
Boko Haram, which translates roughly into "Western education is sinful", has claimed responsibility for almost daily shootings and attacks with homemade bombs in remote northeast Nigeria in recent months.
Two people were shot dead and two others were wounded by a bomb blast on Thursday, in the latest attack by members of Boko Haram, a military Joint Task Force said.
The group, which wants sharia (Islamic law) more widely applied across Nigeria, has killed hundreds of people this year.
Intelligence officials have said there is evidence to suggest some Boko Haram members have trained in Niger but the group has an ill-defined command structure, a variety of people who say speak on its behalf, and an unknown number of followers. (Additional reporting by Ibrahim Mshelizza in Maiduguri and Mark John in Dakar; Writing by Joe Brock; Editing by Tim Pearce)
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