U.S. and European naval officials say pirates have hijacked two European-owned tanker ships off the coast of Somalia.

The officials say a Greek-owned chemical tanker, the MV Nipayia, was seized late Wednesday with 19 crew members on board.  

They say pirates seized the Norwegian-owned MV Bow Asir on Thursday.  That ship is said to have a crew of at least 23.

Both hijackings occurred off Somalia's eastern coast, in the Indian Ocean.

Somali pirates seized more than 40 ships during 2008 and received millions of dollars in ransom payments in a hijacking spree.  

The hijackings have become less frequent since the United States, China, Russia and other nations began conducting anti-piracy patrols in the waters near Somalia.

Some information for this report was provided by AFP, AP and Reuters