(Updates with announcement of sanctions, adds more details, background)

WASHINGTON, Jan 7 (Reuters) -

The United States determined on Tuesday that members of Sudan's Rapid Support Forces $(RSF)$ and allied militias committed genocide in Sudan and it imposed sanctions on the group's leader over a conflict that has killed tens of thousands of people and driven millions from their homes.

U.S. Secretary of State Antony Blinken said in a statement the RSF and aligned militias had continued to direct attacks against civilians, adding that they had systematically murdered men and boys on an ethnic basis and had deliberately targeted women and girls from certain ethnic groups for rape and other forms of sexual violence.

The militias have also targeted fleeing civilians and murdered innocent people escaping conflict, Blinken said.

"The United States is committed to holding accountable those responsible for these atrocities," Blinken said.

Washington announced sanctions on the leader of the RSF, Mohamed Hamdan Dagalo, barring him from traveling to the United States and freezing any U.S. assets he might hold.

"For nearly two years, Hemedti’s RSF has engaged in a brutal armed conflict with the Sudanese Armed Forces for control of Sudan, killing tens of thousands, displacing 12 million Sudanese, and triggering widespread starvation," the Treasury Department said in a separate statement.

Sudan's army and the paramilitary Rapid Support Forces have been locked in conflict for more than 18 months, creating a humanitarian crisis in which U.N. agencies have struggled to deliver relief.

The war erupted in April 2023 amid a power struggle between the Sudanese Armed Forces and the RSF ahead of a planned transition to civilian rule.

(Reporting by Daphne Psaledakis ; Writing by Nafisa Eltahir; Editing by Alison Williams and Gareth Jones)

((Nafisa.Eltahir@thomsonreuters.com;))