Ukrainian President Volodymyr Zelensky said Tuesday that Ukraine had accepted a 30-day ceasefire proposed by the United States, following critical peace talks between US and Ukrainian officials in Saudi Arabia.

The agreement comes after the U.S. and Ukraine met in Saudi Arabia and also agreed to work toward an agreement for developing Ukraine’s critical mineral resources.

Russian forces have begun an assault on the town of Sudzha, the main population center in the Kursk region that was captured by Ukraine last year, a top Russian commander said on Tuesday. The advance puts Moscow on the verge of ending the first invasion of Russian territory since World War II.

Russia said on Tuesday that its troops had made major new gains in its western region of Kursk, accelerating their push to drive out Ukrainian forces who have been clinging on to a slice of Russian territory since last August.