The killing of two Western hostages in northern Nigeria adds a fearsome dimension to the fierce campaign being waged by militant Islamists and heightens concerns they've joined forces with al-Qaida's North African branch.

Al-Qaida in the Islamic Maghreb, the Arabic word for North Africa, specializes in kidnapping foreigners. There have been growing suspicions over the last year that it has extended its operations south to Africa's most populous nation and the continent's leading oil producer.

The hostages, Christopher McManus of Britain and Franco Lamolinara of Italy, were killed by their captors March 8 when a rescue attempt by British and Nigerian Special Forces went wrong in the remote northern city of Sokoto, a centuries-old Muslim trading center.

The men were kidnapped May 12, 2011, in northwestern Nigeria where the Italian construction company they worked for was building the state headquarters of Nigeria's central bank.

Nigerian authorities say an extremist faction of Boko Haram, an Islamic movement that launched an uprising in 2009, was behind the kidnappings after it had been coached by AQIM.

Boko Haram means "Western education is forbidden" in the Hausa language spoken in predominantly Muslim northern Nigeria, where several thousands of people have been killed in clashes between Muslims and Christians, who dominate the oil-rich south in recent years.

Nigeria's population of 150 million is more or less evenly divided between the two religions.

Muslim radicals have been demanding the introduction of Shariah religious law in the northern provinces but demands for a more equitable share of Nigeria's oil wealth, centered in the south, have heightened religious and political unrest.

The McManus and Lamolinara kidnappings were originally claimed by a group calling itself Al-Qaida in the Land beyond the Sahel," the semi-arid belt that runs across Africa south of the Sahara Desert where AQIM operates.

Security officials in Abuja, Nigeria's capital, say the kidnappings suggest that Boko Haram has splintered, with extremists in contact with AQIM behind the abduction and subsequent death of the two Westerners.

"In recent months, Boko Haram has increasingly been seen by Western security services as one of the fastest growing jihadist groups in the Middle East and Africa," the Financial Times reported.

Boko Haram's original leader, a charismatic young preacher named Mohammed Yusuf critical of mainstream Islam and official corruption, was killed in 2009.

But his successors remain at large despite a major crackdown, by security forces.

The group's evolving ideological shift, apparently inculcated by AQIM's veterans, has attracted a strong following among the north's impoverished youth.

"We've been able to link the activities of the Boko Haram sect to the support and training they've received from AQIM," Nigeria's military commander, Air Chief Marshal Oluseyi Petinrin, declared Feb. 23, the first such public comment by a senior security official.

His observations were made at a summit of the 15-member Economic Community of West African States in Abuja.

It ordered security chiefs to draw up "urgent" plans to counter the threats of terrorism and the piracy plaguing the Gulf of Guinea, a major oil zone off West Africa.

Petrinin noted, "The instability in Libya and the activities of AQIM has no doubt had a spillover effect into our sub-region."

AQIM has been extending southward into Chad, Mali, Niger, Mauritania and Bukina Farso over the last few years.

Now it seems to be trying to turn what has been a largely Islamist uprising in northern Nigeria into part of al-Qaida's global jihad at a time when Africa is emerging as a strategic oil producer, with the United States a major importer.

Nigeria is increasingly vulnerable, gripped by political turmoil and rampant corruption, and signs of a resurgent insurgency in the Niger Delta, the main oil producing zone that a couple of years ago cut Nigerian oil output by 40 percent.

Until last year, Boko Haram's activities were restricted to killing Christians and police officers and blowing up churches with crude bombs. But then it began mounting far more sophisticated attacks and for the first time hit foreign targets like the U.N. headquarters in Abuja in 2011.

The hostage slayings has opened a new chapter of terrorism in Nigeria that could connect with other turbulent Muslim areas such as the Horn of Africa and East Africa. Al-Qaida suspects have even been found in South Africa.