An Indian naval vessel sank a suspected pirate "mother ship" in the Gulf of Aden and chased two attack boats into the night, officials said Wednesday, as separate bands of brigands seized Thai and Iranian ships in the lawless seas. The owners of a seized Saudi oil supertanker, meanwhile, negotiated for the release of the ship, anchored off the coast of Somalia. A multinational naval force has increased patrols in the waters between the Arabian Peninsula and the Horn of Africa, where pirates have grown bolder and more violent. The force scored a rare success Tuesday when the Indian warship, operating off the coast of Oman, stopped a ship similar to a pirate vessel described in numerous bulletins. The Indian navy said the pirates fired on the INS Tabar after the officers asked to search it.