ABUJA, Nigeria—Gunmen in Nigeria kidnapped six Filipino workers during an attack on an oil service vessel in the Niger Delta, a private security source said on Saturday.

A speedboat carrying 12 gunmen attacked the vessel and took six hostages, including the boat’s captain and two engineers.

“The vessel was attacked between Port Harcourt and Bonny,” said the source, who asked not to be named.

Reports remained sketchy and the Filipinos and their vessel were not identified.