The military launched a crackdown on suspected militants in Nigeria's restive, petroleum-rich south Friday as militants released another foreign hostage taken in a spate of kidnappings roiling Africa's oil giant.

Bletyn Wikina, a top Rivers State official, said the German man was safely with Nigerian authorities and unharmed. The man, whose name wasn't released, was snatched Aug. 3 from a makeshift checkpoint by gunmen wearing military fatigues.

Wikina didn't say if a ransom had been paid and it was unclear if the release was linked to a new campaign against militants. President Olusegun Obasanjo ordered the clampdown Tuesday and military officials said it began Friday.

Soldiers could be seen entering houses in the main Niger Delta city of Port Harcourt, detaining at least five people. The troops fired in the air, sending men and women screaming through the streets. Gunfire sounded for at least an hour.

"This is the beginning of something bigger to drive all the bandits from the state," said Maj. Sagir Musa, a military spokesman. "It will continue. It is ongoing."

CountryWatch: Nigeria

Port Harcourt has been rocked by a series of kidnappings that has seen 15 foreigners seized in the streets or from nightclubs over the past two weeks. Ten have been released unharmed but five, including an American, remain unaccounted for. Hostages taken by militants looking for ransom are rarely harmed and most end peacefully.

Also Friday, Port Harcourt's main airport closed, cutting off a main entry and exit point to the city for oil-industry workers. Officials blamed a Thursday electrical fire for the closure.

Militant attacks have cut Nigeria's daily oil production by nearly a quarter from its normal 2.6 million barrels. The country is Africa's biggest oil exporter and the fifth-largest supplier of crude to the United States.

Many Nigerians in the region say the violence stems from popular discontent over the portion of Nigeria's oil earnings that returns to their areas.

The Abuja-based federal government apportions the earnings from Nigeria's oil industry. Despite the great riches, most of the Niger Delta is mired in extreme poverty, and most residents live without electricity, health care or schools. Many Nigerians accuse their leaders of stealing much of the oil funds. Nigeria is routinely ranked among the world's most-corrupt nation.