The secret whistleblower complaint that the acting director of national intelligence has refused to hand over to Congress involves President Donald Trump’s “communications with a foreign leader,” The Washington Post reported Wednesday, citing two former U.S. officials familiar with the complaint.

The officials said Trump’s interaction with the foreign leader, whose identity was not disclosed, included a “promise” made by the president that was regarded as concerning by the intelligence official who filed a formal whistleblower complaint with the intelligence community inspector general.

Rep. Adam Schiff (D-Calif.), chairman of the House Intelligence Committee, said in a statement that the inspector general had determined this complaint to be “both credible and urgent.”