May 21 (Reuters) - Critical Metals CRML.O said on Thursday it has signed a 15-year binding offtake agreement with REalloys ALOY.O for rare earth concentrate from its Tanbreez project in Greenland.

Under the agreement, REalloys will buy 15% of annual rare earth concentrate production from the project, which is one of the world's largest known heavy rare earth deposits.

Shares of Critical Metals were up 8% in premarket trading.

• The agreement formalizes and expands on a non-binding deal signed by the companies last October.

• It also follows Greenland's approval in April for Critical Metals to increase its ownership in the project to 92.5%.

• Critical Metals said the deal strengthens the commercial outlook for the Tanbreez project as it moves toward production.

• REalloys will receive priority rights to concentrate containing higher levels of the critical heavy rare earth elements, dysprosium and terbium, along with a right of first refusal over additional volumes.

• Deliveries will be made from the Tanbreez port in southern Greenland, with pricing linked to international rare earth oxide benchmarks.

• United States and its allies have stepped up efforts to secure supplies of critical minerals outside China, which dominates much of the global rare earth processing industry.