One Iranian and one Japanese vessel were reported as being hijacked earlier on Thursday, according to the Kuala Lumpur-based International Maritime Bureau's (IMB) Piracy Reporting Centre.

Noel Choong of the IMB said the German-operated cargo ship was seized Thursday in the Gulf of Aden off the Somalian coast. He added that the hijacking occurred hours after a Japanese-operated tanker and an Iranian ship off the coast of Somalia were hijacked in the same area.

Choong said three hijackings in a day was "unheard of." So far seven ships have been hijacked in the important African shipping lane since June 20.

Choong, who heads IMB's piracy reporting center in Kuala Lumpur, strongly urged the United Nations "to take serious action to stop this menace."

The waters off Somalia are notorious for piracy, with the IMB reporting 24 attacks on vessels there between April and June this year.

Two German citizens seized from their yacht off Somalia in late June were recently released after being held for six weeks.