Gunmen have abducted four Catholic nuns in southeast Nigeria’s Imo state, police said Monday, in the latest violence in a region where separatist tensions are on the rise. Kidnappings by criminal gangs are frequent in Africa’s most populous country, but in recent weeks members of Christian churches have increasingly been targeted. Most hostages are released after a ransom payment, but some have been killed. “Four reverend sisters of the Catholic church were abducted,” Imo state police spokesman Michael Abattam told AFP. He said the nuns were seized near Okigwe city on Sunday on their way to mass. “We are on the trail of the kidnappers with a view to freeing the victims,” he said. Abattam could not immediately say what the motive was for the abduction as no group has claimed responsibility. Southeast Nigeria has seen a surge in violence blamed on the outlawed Indigenous People of Biafra (IPOB) group or its armed wing ESN. IPOB which seeks a separate state for ethnic Igbo people has repeatedly denied responsibility for violence in the region. More than 100 police officers and other security personnel have been killed since the beginning of last year in targeted attacks in the region, according to local media tallies. Prisons have also been raided with scores of inmates freed and weapons stolen. IPOB’s leader Nnamdi Kanu is in government custody since and faces trial for treason. Separatism is a sensitive issue in Nigeria where the declaration of an independent Republic of Biafra in 1967 by Igbo army officers sparked a civil war that left more than one million people dead.