Lagos: As many as 23 Indian sailors were being held hostage since Tuesday night by pirates who hijacked an oil tanker with a Singapore-based company in southwest Nigeria's Lagos State port, the firm said.

The 23 Indian sailors are on board the hijacked oil tanker, the oil tanker company Pioneer Ship Management Services LLC told Xinhua.

The International Maritime Bureau (IMB) said in a statement that armed pirates boarded the vessel Tuesday night, attacking the crew members.

The pirates forced the ship to sail into the open sea, the IMB added.

The frequent attacks on ships by pirates in the Gulf of Guinea pose an increasing threat to the trade hub.

IANS