MAIDUGURI, NIGERIA ¨C Islamic State claimed responsibility on Wednesday for an attack on the convoy of a state governor who was headed to a rally in northeastern Nigeria ahead of Saturday¡¯s presidential election.

The group said in a statement on its Aamaq news agency that 42 people were killed in Tuesday¡¯s attack on Borno state¡¯s governor. Official sources told Reuters earlier on Wednesday between three and 10 people were killed, and that some of them may have been beheaded.

Boko Haram has waged a decade-long insurgency in Nigeria¡¯s northeast which has killed around 30,000 people and forced about 2 million to leave their homes. Islamic State West Africa Province, which split from Boko Haram in 2016, has carried out a series of attack on military targets in the last few months.

Security sources said earlier on Wednesday the gunmen opened fire on the motorcade transporting Borno¡¯s state governor, Kashim Shettima, on his way from state capital Maiduguri to the market town of Gamboru for a rally.

Two security sources said three people died. A government and a separate security source said as many as 10 people were killed. Some of those killed may have been beheaded, they said.

There was no indication of how Shettima, a government politician, was affected by the attack. His spokesman could not be reached for comment. A security source said the convoy had returned to Maiduguri.

Borno, the birthplace of Boko Haram, has been the state worst hit by Islamist insurgents.

Incumbent Muhammadu Buhari is seeking a second term in office in Saturday¡¯s elections in Nigeria, Africa¡¯s biggest democracy. He faces a tight contest against his main challenger, Atiku Abubakar, a businessman and former vice president.