Lagos: A radical Muslim sect responsible for assassinations and bombings across northern Nigeria may be trying to link with two al-Qaeda-linked groups in other African countries to mount joint attacks in this oil-rich nation, the commander for US military operations in Africa said on Thursday.

Gen Carter Ham said "multiple sources" indicate the Nigerian sect known as Boko Haram made contacts with al-Qaeda in the Islamic Maghreb, which operates in northwest Africa, and with al-Shabab in Somalia.

"I think it would be the most dangerous thing to happen not only to the Africans, but to us as well," Carter said.

Ham said there is no specific intelligence suggesting the groups plan attacks against US or Western interests in Nigeria, but the nation is a major supplier of crude oil to the US and is an economic hub drawing foreigners from across the world.

Ham's comments were the strongest official remarks on fears privately held by Western and Nigerian officials.

However, it remains unclear what formal links, if any, exist between Boko Haram, al-Qaeda in the Islamic Maghreb and al-Shabab. The three organisations have different ethnic roots and their objectives are not the same, but they are all Islamist militant groups.

Boko Haram, whose name means "Western education is sacrilege" in the local Hausa language, came to prominence in 2009 when sect members attacked local police stations and government buildings throughout northeast Nigeria.

The riots and ensuing security crackdown left 700 people dead. Last year, the group began assassinating clerics and police officers. It also has engineered spectacular attacks, including the June bombing of Nigeria's federal police headquarters, the assassination of a prominent politician and a prison break that freed more than 700 inmates.

Boko Haram seeks the implementation of strict Shariah Islamic law in the country.