Sen. Marco Rubio (R., Fla.) and Rep. Mike Pompeo (R., Kan.) initially presented Lynch in October with a series of questions about how the cash payment to Iran was approved and delivered.

In an Oct. 24 response, Assistant Attorney General Peter Kadzik responded on Lynch’s behalf, refusing to answer the questions and informing the lawmakers that they are barred from publicly disclosing any details about the cash payment, which was bound up in a ransom deal aimed at freeing several American hostages from Iran.

The response from the attorney general’s office is “unacceptable” and provides evidence that Lynch has chosen to “essentially plead the fifth and refuse to respond to inquiries regarding [her] role in providing cash to the world’s foremost state sponsor of terrorism,” Rubio and Pompeo wrote on Friday in a follow-up letter to Lynch, according to a copy obtained by the Free Beacon.

The inquiry launched by the lawmakers is just one of several concurrent ongoing congressional probes aimed at unearthing a full accounting of the administration’s secret negotiations with Iran.