* Islamist bombings cause carnage in north, central Nigeria
* Militants still holding over 200 abducted school girls
* Boko Haram main security threat to Africa's top economy
By Lanre Ola and Imma Ande
MAIDUGURI/YOLA, Nigeria, June 1 (Reuters) - A bomb blast targeting a television viewing centre for football in northeast Nigeria killed at least 14 people and wounded 12 on Sunday, police and the military said.
There was no immediate claim of responsibility for the blast in Gavan in the Mubi area of Adamawa state. Islamist militant group Boko Haram, whose struggle for an Islamic state is concentrated in the Northeast, would be the prime suspect.
"So far we have 14 dead while 12 are injured, some of them critically," police spokesman for Adamawa state Usman Abubakar said by telephone. He had no further details.
The group has set off several bombs across north and central Nigeria over the past two months, repeatedly causing carnage.
"I heard a loud blast. The place is near the market, which I had just left. I ran," said John Audu, a resident of the town.
Last weekend, a suicide bomber set out to strike an open-air viewing of a football match in the central city of Jos, but his car blew up before reaching the target, killing three people.
A suicide bombing the week before in Jos killed 118 people, and two bombs on the outskirts of Abuja in April killed 95 between them. Boko Haram, now seen as the main security threat to Africa's biggest economy and top oil producer, has killed thousands since launching an uprising in 2009.
The group is still holding more than 200 schoolgirls that it abducted on April 14, sparking international outrage.
Nigeria's president said on Thursday he had ordered "a full-scale operation" against Boko Haram and sought to reassure parents of the kidnapped girls that their children would be freed.
Since the girls were taken, Boko Haram fighters have killed at least 500 civilians, according to a Reuters count.
Two Italian priests and a Canadian nun, kidnapped in northern Cameroon nearly two months ago by suspected Boko Haram gunmen, were released on Sunday, smiling and apparently in good health as they arrived in the capital.
Cameroonian security forces killed some 40 Boko Haram militants in clashes in the country's far north, state radio said on Sunday. A presidency source confirmed the clashes, which took place west of the town of Kousseri, in the region bordering Nigeria and Chad.
Nigeria has accused Cameroon of not being tough enough on the militants hiding in its border region.
(Writing by Tim Cocks; Editing by Cynthia Osterman and Mohammad Zargham)