The families of merchant seamen held by Somali pirates for more than 18 months say the crew members are being forced to call home with warnings they could suffer further abuses unless a $2.85 million ransom is paid soon.

The payment for the 22 crew members on the Malaysian-owned MV Albedo was due in April under a deal negotiated through Dubai-based Somali merchants.

Families across South Asia raised some of the amount and the deadline was extended to await the remaining share from the ship's owners.

Shahnaz Jawaid, wife of the Albedo captain, says families of the crew receive calls pleading for the money nearly every day. Jawaid spoke from Karachi, Pakistan, on Thursday.

The Kenya-bound ship was hijacked in November 2010 in the Gulf of Aden.