Warri - Four people were killed by gunmen in southeast Nigeria, police said on Saturday, after a week of clashes with security forces as inter-community tensions rise in the former Biafra region.The attack appeared to target a market and mosque in a neighbourhood of the city of Asaba inhabited mainly by the Hausa and Peul ethnic groups, who are originally from northern Nigeria."Three armed men, all in black outfits, suspected to be members of a cult group or Indigenous People of Biafra (IPOB) fired indiscriminately into Abraka market at Asaba... and in the process killed four persons," a local police statement said. Five others were wounded.The IPOB is demanding an independent state for the Igbo people, the most populous ethnic group in Nigeria's southeast.Hassan Farouk, who sells yams in the market, told AFP that "it happened about 11 pm on Friday. Over 20 armed members of IPOB invaded our mosque at Cable Point and threw an explosive into the mosque, but fortunately, it did not explode".'Deeply worrying' He said they raised the alarm "and the attackers all moved straight to the Hausa market, also called Abraka market, and killed four people."The southeast has seen a resurgence of violence over the past week, a situation Amnesty International has called "deeply worrying".Nigeria, which is almost evenly split between a predominantly Muslim north and largely Christian south, is a country of barely concealed religious and ethnic tensions.Violence frequently erupts but Biafra is a particularly sensitive issue as a previous unilateral declaration of independence by the region in 1967 sparked a brutal, 30-month civil war.More than one million people were killed, most of them Igbos.On Thursday a police chief was torched in Aba, the epicentre of the recent violence, while on Wednesday a police officer was killed in Port Harcourt, capital of Rivers state, and 32 pro-Biafra supporters were arrested.The IPOB have denounced violent repression against them, claiming soldiers killed several of their members in recent days - a charge the army denies.On Friday, Abuja branded the IPOB, whose leader Nnamdi Kanu is accused of treason, as a "terrorist organisation".Kanu has vowed a non-violent approach to force a referendum on self-determination.