ABUJA, Nigeria — Gunmen attacked a vessel off the coast of Nigeria’s oil-rich southern delta, kidnapping six foreigners in an area that has become increasingly dangerous for oil companies and shippers, a police official said Wednesday.

Three Ukrainians, two Indians, and a Russian were taken from a vessel run by energy company Century Group 43 miles off Nigeria’s southern coast on Sunday, Bayelsa police spokesman Fidelis Odunna said. The kidnappers have demanded a $1.27 million ransom.