WASHINGTON — The White House wants to know who leaked President Donald Trump’s briefing papers to the press and thereby let it be known publicly that advisers had recommended against offering congratulations to Russian President Vladimir Putin.

Republicans and others have criticized Trump for congratulating Putin on his re-election, which some observers have rejected as a rigged vote.

A White House statement issued Wednesday warned that it would be a firing offense and likely illegal to leak the president’s briefing papers. An internal investigation is underway.

In the case of the call Trump made to Putin, the briefing papers included the guidance, in capital letters, “Do not congratulate.” That’s according to a senior administration official who wasn’t authorized to discuss internal matters and spoke to The Associated Press on condition of anonymity.