Militants who kidnapped nine foreign oil workers in a flurry of attacks that forced a 20 percent cut in Nigerian crude exports vowed Sunday to escalate the violence, threatening for the first time to fire rockets at international oil tankers.

While the military said tankers in Nigerian waters were safe, the West African nation is reeling from militant attacks that blasted oil and gas pipelines Saturday, damaged a key oil loading terminal and halted the flow of more than 500,000 barrels a day.

Nigeria is Africa's leading oil exporter and the United States' fifth-largest supplier, usually exporting 2.5 million barrels daily.

Efie Alari, who identified himself as commander of the Movement for the Emancipation of the Niger Delta, told The Associated Press by telephone Sunday his group was poised to attack foreign oil tankers offshore.

"We'll use our rockets on the ships to stop them from taking our oil," Alari said. His identity could not be independently verified, but the call came from a number used previously by the group based in the oil region of the Niger River delta.

The military said it would do whatever was necessary to ensure the safety of tankers.

"I don't know their capabilities, but we're not leaving anything to chance," said Maj. Said Hammed, a spokesman for the military task force in the delta. "The assurance has been given at the highest level of government that oil tankers are safe in Nigerian waters. That assurance remains."

Violence and sabotage of the delta's oil operations have been common for 15 years amid demands by the region's impoverished communities for a greater share of oil revenue flowing from their land.

Kidnappings are also a common occurrence in the volatile area. Most hostages are released unharmed. Last month, militants held four foreigners for 19 days before releasing them unscathed.

Dozens of militants seized nine foreigners Saturday in an assault in the swampy Forcados estuary after storming a barge belonging to the Houston-based oil services company Willbros, which was laying pipeline for Royal Dutch Shell.

The hostages included three Americans, two Egyptians, two Thais, a Briton and a Filipino, militants and Willbros officials said.

Militants said in an e-mail to AP that they had not decided what to do with the hostages.

"They are being moved around with our units and may likely only be killed in a crossfire" with government forces, the militants said. "We have not reached a decision on what to do with these individuals, but it is difficult to tell what may happen in the coming days. The next few days will determine what steps we will take."

Nigerian President Olusegun Obasanjo called a crisis meeting late Saturday with security chiefs and said "everything possible is already being done to secure the speedy release of the hostages through dialogue," Information Minister Frank Nweke said.

Nweke called on "the so-called militants and hostage takers in the Niger Delta to abandon their criminal activities ... these actions must be condemned by all persons of goodwill within and outside the country."

The militants said they staged Saturday's attacks after a series of military helicopter strikes on ethnic Ijaw villages. The military said the assaults targeted only people stealing oil on barges in the area.

Hammad said no soldiers were killed Saturday, contrary to some Nigerian newspaper reports that five died. No violence was reported Sunday.

The attack that damaged Shell's Forcados oil loading platform forced the company to shut off 400,000 barrels daily. Shell also evacuated staff from a nearby offshore platform, halting an additional 115,000 barrels a day.

A Shell pipeline was blown up Saturday by the delta's Chanomi Creek, and industry officials said militants destroyed a state-run pipeline that feeds natural gas from the Escravos gas plant in the delta to the country's commercial capital, Lagos.

On Sunday, Thai Foreign Ministry spokesman Sihasak Phuangketkeow confirmed the identities of two of the kidnap victims as Somsak Mhadmho, 43, and Arak Suwanna, 33, both of Bangkok, Thailand. Sihasak said both men were married.

Britain's Foreign Office said the kidnapped Briton was John Hudspith of southern England. U.S. officials confirmed three American oil workers were among those kidnapped, but did not identify them.

(Source: AP)