PORT HARCOURT, Nigeria, Jan 23 (Reuters) - Gunmen in speedboats attacked an oil supply vessel contracted to U.S. oil major Exxon Mobil <XOM.N> in the restive Niger Delta, military and security sources said on Friday.

Ten armed men in two speedboats attacked the MV Ngoni off the coast of the Niger Delta, the heart of Nigeria's oil and gas sector, early Friday morning.

There were no fatalities or kidnappings, but some items were stolen from the vessel, a private security source said.

"I can confirm there was an attack," said Lieutenant-Colonel Sagir Musa, spokesman for the military task force in the southern state of Rivers.

Musa said he didn't believe the offshore attack was near an oil facility.

Insecurity in the region has cut Nigeria's oil output by around a fifth and has led foreign companies in sectors from construction to telecoms, as well as the oil industry, to reconsider investments and reduce expatriate staffing.

The Niger Delta has long been plagued by violence but the number of attacks on vessels this year and abductions in areas previously considered relatively safe has alarmed the security forces.

Friday's attack was the ninth such attack on shipping in waters off the delta this year.

(For full Reuters Africa coverage and to have your say on the top issues, visit: http://africa.reuters.com/ ) (Reporting by Austin Ekeinde; Writing by Randy Fabi; Editing by Jon Boyle)

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