Eight foreign oil workers abducted by Niger Delta militants were freed several hours later, a Nigerian military spokesman said Sunday.

The eight were released overnight Saturday, the spokesman was quoted by the BBC as saying, but he disputed allegations that a ransom was paid.

There was no official confirmation given as to the nationality of the foreign workers, though initial speculation was the abductees had been Russians.

The eight were taken after an attack on an oil tanker early Saturday. Two people were shot dead and two crew members were wounded in the attack using speedboats, BBC radio reported.

It was the second such attack within 24 hours - on Friday militants abducted five Russians on board a Swedish vessel sailing to the Akpo oil field.