An upsurge of militant and criminal activity in southern Nigeria has cut production by about one quarter in Africa's biggest producer.

Over 200 foreigners have been kidnapped in the oil-pumping region since December 2005, including over 100 this year alone. Most of those kidnapped are quickly released after ransoms are paid.

Here's a look at some recent developments:

—July 5: Gunmen attack a car carrying a 3-year old British girl to school in Port Harcourt, smashing in the windows with rifle butts and kidnapping the toddler.

—July 4: Attackers hit a Royal Dutch Shell oil rig on an island in a remote area of the Niger Delta, kidnapping an Australian, two New Zealanders, one Lebanese and one Venezuelan. The region's main militant group, the Movement for the Emancipation of the Niger Delta, says it won't extend a unilateral, one-month cease fire.

—June 21: Troops attack gunmen occupying an oil facility and holding two dozen workers and soldiers hostage. The clash leaves a dozen of gunmen dead.

—June 3: Gunmen dynamite housing for foreign workers for an aluminum-smelting factory, kidnapping six Russians.

—June 2: Movement for the Emancipation of the Niger Delta announces unilateral truce to allow government of new President Umaru Yar'Adua to negotiate long-term peace for the region.

—May 16: Attackers dynamite the country retreat of Vice President Goodluck Jonathan, whose inclusion in the new government is meant to help calm the region from which he hails.

—May 15: Shell says protesters seeking oil revenues occupied an oil-pipeline switching facility, causing oil production cuts of 170,000 barrels per day.

—May 8: Movement for the Emancipation of the Niger Delta bombs three major oil pipelines.

—May 3: At least 21 workers, mostly foreigners, are kidnapped in separate attacks that leave one Nigerian soldier dead.

—April 27: Gunmen shoot dead two policemen in Port Harcourt during a failed attempt to kidnap two foreign oil workers working for French oil company Total SA.