Armed gunmen attacked an oil rig in Nigerian waters forcing the operator, Royal Dutch Shell, to shut down production in the area. In a separate but related incident, militants attacked a boat briefly taking a U.S. national aboard hostage. For VOA, Sarah Simpson has more from Lagos.

Royal Dutch Shell confirm that gunmen attacked one of their oil rigs in Nigeria in the early hours of Thursday morning. The attack forced the oil giant to shut down oil production in the area - reducing its daily output by 200,000 barrels.

This latest attack significantly reduces Nigerian crude production, already well below capacity due to sustained attacks from militant groups.

A Nigerian separatist militant levels his machine gun at reporters from his war boat on the Escravos River in southern Nigeria (File)

Nigeria's main militant group, the Movement for the Emancipation of the Niger Delta, or MEND, claimed responsibility for the attack in a statement issued to journalists.

MEND also says it took a US national hostage Thursday in a separate incident. The group said later it released the hostage without conditions. Private security officials confirmed the man's release.

Hostage taking for ransom is common in the Niger Delta.

Attacks on offshore facilities are rare. Many oil industry officials consider offshore operations to be safer than operating onshore in the Niger Delta. However, a written statement, MEND said it wanted to demonstrate that no oil facility, even one's offshore, is safe.

In MEND's words, "The location for today's attack was deliberately chosen to remove any notion that off-shore oil exploration is far from our reach." The rig attacked on Thursday lies some 100 kilometers out to sea in the Bonga oil field.

The Niger Delta remains poor despite decades of oil production. The delta is awash with guns and much of the simmering anger in the region is directed towards the oil industry.