Brussels, Belgium ? Pirates armed with machine guns hijacked a Norwegian chemical tanker Thursday off the coast of Somalia, the ship’s owner said, an attack that came less than 24 hours after a smaller Greek-owned vessel was seized in the same area.

The U.S. 5th Fleet, which patrols the pirate-infested Gulf of Aden, confirmed both hijackings and said they took place in the same area but separate from the gulf, one of the world’s busiest — and now most treacherous — sea lanes.

The 23,000-ton Norwegian-owned Bow Asir was captured 250 miles off the Somali coast on Thursday morning, and the 9,000-ton Greek-owned Nipayia, with 19 crew members, was seized 450 miles off Somalia on Wednesday afternoon, the European Union’s military spokesman said.