WARRI, Nigeria (AP) — Police in southern Nigeria say three people have been rescued and two others remain hostage after gunmen attacked a passenger bus.

Nnamdi Omoni, spokesman of the Rivers state police command said Monday that there was a heavy firefight between police and the kidnappers. He said the bus driver was wounded in the attack.

Kidnappings of Nigerians and foreigners are common all over the country. In the oil-rich southern Niger Delta, they are carried out by ordinary criminals as well as militants demanding a greater share of oil earnings for locals. Hostages are usually released unharmed after ransom payments.

Last month, 15 passengers were seized from a Lagos-bound bus near Rivers state but all of them were later released. It was not clear if ransoms were paid.