Gulf states who have yet to ratify an agreement on a single currency for the region are being called upon to do so by the end of this year, an Oman finance ministry official said on Saturday.

Only four of the Gulf Co-operation Council's (GCC) six member states are taking part in monetary union after the United Arab Emirates opted out in May, three years after Oman did the same.

"The GCC countries have asked those who have not ratified the single currency to do so by the end of the year," Darwish Ismail Al-Balushi, secretary general in the Oman finance ministry, told Reuters.

Ratification by the four remaining countries is needed for the project to go ahead, but so far only Saudi Arabia has done so. Bahrain, Qatar and Kuwait have not yet ratified, leaving question marks over the future of the project.-Reuters