LAGOS (Reuters) - For a long time it seemed the violent Islamist groups plaguing Nigeria were more interested in their grievances with the government than in any global jihad against Western "infidels".
The killing of seven foreign hostages in Nigeria this week - confirmed by Italian and Greek authorities although not by Nigeria's government itself - showed that, increasingly, this is no longer the case.
Ansaru, an obscure group that had seemed to operate on the margins of the main Islamist insurgency labelled Boko Haram, is emerging as a much more explicit threat to Western interests.
That threat will only grow as relations between al Qaeda-linked Islamist groups in Africa's vast Sahara region and some home-grown Nigerian militants flourish.
"It is now clear some Nigerian groups are hand in hand with terrorist organisations in the sub-region. You can no longer separate Nigeria from terrorism across Africa," said Charles Dokubo of the Nigerian Institute of International Affairs.
Ansaru announced on Saturday that it had killed a British, an Italian, a Greek and four Lebanese construction workers they had abducted in northern Nigeria's Bauchi state last month. It said this was because of efforts by British and Nigerian security forces to forcibly rescue them.
Greece and Italy confirmed the news on Sunday and Britain said it was likely to be true. Nigerian officials have declined to confirm or deny it. Ansaru has posted a video online of what it said were the bodies.
Unlike the better known Boko Haram, whose main fight is with Nigeria's government and which normally strikes domestic targets like police stations, politicians or Nigerian Christians, Ansaru is explicitly focused on jihad (holy war) against the West.
While Boko Haram wants an Islamic state in religiously-mixed Nigeria - Africa's most populous state and biggest oil producer, Ansaru sees the country as launch pad for reprisals against the West over its involvement in places like Mali.
Intelligence sources say Ansaru is smaller and more focused than Boko Haram, whose movement is increasingly fragmented.
It has also forged much more direct ties with al Qaeda in the Islamic Maghreb (AQIM), the Algerian-born outfit that French forces chased out of towns in the northern desert of Mali last month.
"Links between them and AQIM are much clearer than links between Boko Haram and AQIM," said a security official in Abuja.
"They came out of the same seed as Boko Haram, but there was a difference in ideology. Their ideology is closer to AQIM's."
That difference became clear in January 2013, when Boko Haram - whose Hausa-language name means "Western education is sinful" - carried out a major attack on the north's biggest city of Kano that killed 186 people.
Ansaru, then largely unknown to authorities, explicitly broke away from Boko Haram, denouncing the attack because it said most of the victims were Muslims. Nonetheless, security officials say it retains loose operational ties with Boko Haram.
Its full name - Jama'atu Ansarul Musilimina Fi Biladis Sudan - means "Vanguards for the Protection of Muslims in Black Africa". Analysts say this shows it wants to be seen as distinct from AQIM, which is run by mainly Arab Algerians.
Ansaru claimed a dawn raid on a police station in Abuja last year, where it said hundreds of prisoners were released.
It has since risen to prominence with several high-profile attacks and kidnappings, including an ambush of Nigerian troops heading to Mali from central Nigeria in January, in a place hundreds of miles from its base in the north's main city Kano.
The survival rate of hostages seized by Ansaru is low. The group was suspected of being behind the killing of a British and Italian hostage a year ago in northwest Nigeria during a botched attempt to rescue them by British and Nigerian forces.
It also claimed responsibility for the kidnapping in December of a French national, still missing. Why it so readily kills the hostages it goes to such lengths to seize is not clear, although it is standard in jihadist manuals that hostages are to be killed in the event of a rescue attempt. A German killed by another al Qaeda-affiliated group last year also died when their house was raided.
"The last time they killed hostages, it was clearly a blunder by the Nigerian forces. I have a strong suspicion these deaths were caused by something similar," said Mohammed Junaidu, a northern opposition politician and former legislator.
Italy and Greece have both denied there was any attempt to free the seven. Britain has remained quiet.
Rivalry between Ansaru and Boko Haram could push the latter to take a more international outlook. Boko Haram claimed a bombing of the U.N. Nigeria headquarters that killed 25 people in August 2011 - although intelligence officials believe it may have been planned by fighters who now belong to Ansaru.
A group claiming to be Boko Haram claimed the kidnapping of a French family in northern Cameroon last month - the first time they have been directly linked with abducting Westerners.
"While Boko Haram's campaign was driven by domestic factors during its formative years, there are growing risks that some elements within (it) will also adopt a more transnational approach, increasing targeting of foreign interests," said Roddy Barclay, Africa analyst at Control Risks.
Editing by Mark Heinrich