Nigerian military officials confirmed an oil spill in the Niger Delta, but did not cite a cause of the spill and said that military forces had not encountered rebels there. Rebels have attacked three Shell (RDS-A) assets in Nigeria since June. Shell confirmed Tuesday's attack, but said production was not interrupted because its facility was not currently involved in the production process.

After breaking a cease-fire agreement with the government in late January, Nigerian rebels promised to step-up their attacks on the country's oil assets. The rebels are seeking the departure of international oil firms from their country, the second-largest oil producer in Africa behind Angola.

The attacks come at an especially bad time for Nigeria, whose temporary president Goodluck Jonathan is trying to show international oil producers that stability in the Niger Delta is improving in the hopes of procuring more investment in his country's oil industry. Nigeria is an OPEC member.