Kidnappers have released the elderly mother of a senior legislator in Nigeria's oil-producing Bayelsa state after holding her for 10 days, a state government spokesman said on Friday.

Gunmen had abducted the mother of the speaker of the Bayelsa state house of assembly from her home on the night of July 24, the latest in a spate of abductions of relatives of powerful people in the anarchic Niger Delta.

"The lady has just been released. She is on the high seas on her way back to Yenagoa," said chief press secretary to the Bayelsa governor Ebimo Amungo, referring to the state capital.

He said no ransom had been paid.

The Niger Delta is home to Africa's biggest oil industry, exporting over 2-million barrels of crude a day and accounting for more than 90% of Nigeria's export earnings.

The impoverished region has become increasingly dangerous since early 2006 when armed groups demanding control over oil revenues stepped up attacks.

Oil output is down by about a fifth because of their raids on production facilities.

However, numerous criminal gangs have seized the opportunity to carry out abductions for ransom, armed robberies and other crimes that have nothing to do with the political struggle of delta militants.

The past few months have seen an increase in child abductions as well as kidnappings of relatives of senior officials - trends which have been widely condemned in Nigeria.

At least 12 foreigners are being held captive by armed groups in various parts of the delta.