Four Roman Catholic priests who were kidnapped by gunmen in southern Nigeria last week have been rescued, police said on Tuesday. The priests were kidnapped on November 6 near a border community between Edo and Delta states in the oil-rich Niger delta region, where kidnapping for ransom is common. "They were rescued by a combined team of police operatives from both Edo and Delta states last Friday at the Delta State University community of Abraka," Delta State police commissioner Muhammad Mustafa told AFP.The incident took place less than three weeks after five Catholic nuns were kidnapped by gunmen in Delta State. The five, abducted as they were coming back from a burial, were released two weeks later, and one person has been arrested, a police spokesperson said.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and FacebookIn January, Nigeria's bishops denounced a wave of kidnappings for ransom.Despite being rich in oil, Nigeria's south is blighted by poverty. Business executives, prominent pastors and the family of leading politicians have been targeted by gangs in the past. In recent years, the phenomenon has spread to northern Nigeria.Amnesty International said in July the northern state of Zamfara was "at the mercy" of armed bandits who take hostages and raid villages.The kidnappings are just one security concern putting pressure on Nigerian President Muhammadu Buhari, who is seeking a second, four-year term in February presidential polls.