LONDON — A cargo ship and a chemical tanker have both been hijacked by pirates in the waters off the coast of Somalia, bringing to four the number of ships seized in the past week, officials said Saturday.

The multiple hijackings indicate that piracy remains a serious problem a year after an international naval armada began deploying off Somalia to protect shipping.

The British-flagged Asian Glory was taken late Friday roughly 600 miles east of Somalia, said Commander John Harbour, a spokesman with the European Union task force charged with combating piracy off Somalia.

The same day, the Singaporean-flagged Pramoni, a chemical tanker with a crew of 24, was seized by pirates in the heavily defended Gulf of Aden, one of the world's busiest waterways.

Harbour said the Asian Glory's crew of 25 — from Ukraine, Bulgaria, India and Romania — appeared to be safe and that the pirates had not yet made contact with the ship's owner, Zodiac Management Agencies.

Somali pirates have hijacked more than 80 ships in the past two years, with many of the seizures earning the pirates multi-million-dollar ransoms. Pirates now hold 14 vessels and close to 300 crew members.

Officials said the Pramoni was traveling east toward India when it was seized. The ship's master radioed that the crew — from Indonesia, China, Nigeria and Vietnam — was safe. The vessel is now also heading toward Somalia.