Nigerian authorities are hopeful that foreign workers being held in the oil-rich Niger Delta would be released soon. Gilbert da Costa reports for VOA that negotiations are ongoing.

A spokesman for the Nigerian army in the main oil city of Port Harcourt, Major Sagir Musa, says progress has been made in negotiating the release of all kidnapped foreign workers and they could be freed as early as Friday.

"Negotiation is ongoing, by all the security agencies, including the state government. I am optimistic, I am confident that before the end of the day, they will be released," he said. "Remember, some were released yesterday or day before."

Militants in Nigeria's troubled Niger Delta are holding some 12 foreigners kidnapped in the troubled southern region on Wednesday and Thursday.

Police confirmed that three South Koreans and eight Filipino workers were seized on their way to work at a power station outside Port Harcourt on Thursday, by militants.

About six policemen escorting the foreigners were killed in the attack. Another expatriate, presumed to be a Dutch, was snatched from a bar in Warri, another oil city, on Wednesday night.

The Philippines has ordered the return of 45 Filipino construction workers from Nigeria after eight were abducted.

Nigeria is Africa's largest oil producer with a daily crude production of 2.6 million barrels.

But an unrelenting spate of kidnappings has crippled the oil industry, forcing the evacuation of thousands of foreign workers since last year and prompting oil output to reduce by 25 percent.

Nearly 200 foreign workers have been kidnapped in the past year in the volatile region. Most of them were released after a ransom payment.

More than 20 workers, most of them foreigners, were abducted in three separate attacks in the delta on Thursday. Eight foreigners and a Nigerian driver were later released.