HOUSTON — The Trump administration delivered a setback to Exxon Mobil on Friday, announcing that it would not grant the oil giant a waiver from sanctions against Russia that would allow drilling in the Black Sea.

The decision, reinforcing barriers erected by the United States over Russia’s intervention in Ukraine, was another sign that President Trump has been unwilling or unable to improve relations with the Kremlin early in his term, after pledging as a candidate that he would seek a thaw.

“In consultation with President Donald J. Trump,” Treasury Secretary Steven Mnuchin said in a terse, prepared statement, “the Treasury Department will not be issuing waivers to U.S. companies, including Exxon, authorizing drilling prohibited by current Russian sanctions.”

The prospect of a waiver had drawn denunciations from both Democratic and Republican lawmakers. When news of Exxon Mobil’s proposal emerged this week, Senator John McCain, Republican of Arizona, wrote in a Twitter post, “Are they crazy?”