U.S. President Donald Trump said on Friday he will nominate U.S. Deputy Secretary of State John Sullivan to be the U.S. ambassador to Russia.

If confirmed by the Senate, Sullivan will be the top U.S. diplomat in Russia at a particularly challenging time for Trump's presidency, which is facing an impeachment inquiry after Trump pressed Ukrainian President Volodymyr Zelenskiy to investigate his domestic political rival, former Vice President Joe Biden.

Trump said in August that Sullivan "could very well be" his nominee to replace then U.S. ambassador to Russia Jon Huntsman, who had announced his resignation earlier that month, amid speculation that he will run for Utah governor.

Huntsman said in a letter in early August that he had notified the president and Secretary of State Mike Pompeo about his decision to end the two years of service to "reconnect with our growing family and responsibilities at home."

Sullivan had also been under consideration to be Trump's national security adviser, a role that ultimately ended up going to Robert O'Brien, the former U.S. special envoy for hostage affairs.

Sullivan took his current post in May 2017. Previously in his career, he had served as deputy secretary of commerce and held senior positions in justice, defense and commerce departments, according to the statement.

Sullivan has been a career U.S. diplomat since 1990, with posts in Ukraine, the U.S. mission to the EU, South Korea, and Honduras.

Huntsman left the post last week. His resignation came during a difficult period of U.S.-Russia relations.

Moscow has come under fire from Washington most recently because U.S. intelligence agencies concluded that Russia interfered in the 2016 presidential elections. Russia has denied wrongdoing. The two countries have been at odds over issues of Ukraine, Syria and arms control, among others.

(With input from Reuters, Xinhua)