Unknown assailants attacked an oil installation in restive southern Nigeria and some crude production has been lost, Royal Dutch Shell PLC officials said Saturday, according to AP. Shell spokesman Precious Okolobo said the attackers hit a flow station belonging to Shell's joint venture in southern Nigeria late Friday and that some oil production had been shut down. He gave no further details. Flow stations are intersections for tubes carrying oil from wells to export terminals. The region's main militant group, the Movement for the Emancipation of the Niger Delta, did not immediately reply to an e-mail seeking comment or claims for the attack.