The acting attorney general informed the Trump White House late last month that she believed Michael Flynn had misled senior administration officials about the nature of his communications with the Russian ambassador to the United States, and warned that the national security adviser was potentially vulnerable to Russian blackmail, current and former U.S. officials said.

The message, delivered by Sally Q. Yates and a senior career national security official to the White House counsel, was prompted by concerns that Flynn, when asked about his calls and texts with the Russian diplomat, had told Vice ­President-elect Mike Pence and others that he had not discussed the Obama administration sanctions on Russia for its interference in the 2016 election, the officials said. It is unclear what the White House counsel, Donald McGahn, did with the information.