The vessel, carrying coal, was seized by pirates last weekend, reported Bernama, the official Malaysian news agency reported.

"We received the reports Monday that the Greek ship ... has been seized by pirates," Andrew Mwangura, coordinator of the East Africa Seafarers Assistance Program, told the Xinhua, China (OTCBB:XHUA)'s official news agency. "The vessel was carrying coal but we don't know whether the Greek ship was sailing from South Africa or not."

Mwangura said officials weren't sure whether the vessel was hijacked Saturday or Sunday.

The International Maritime Bureau reported more than 50 attacks or attempted attacks in or near the Gulf of Aden this year, up from 13 last year, Bernama reported.