The Pentagon said the House of Representatives did not have a resolution authorizing an impeachment investigation, adding that it could not produce documents in the eight days it was given to comply with the subpoena.
Afghan leaders including President Ashraf Ghani have been increasingly critical of the apparent draft deal reached between US special envoy Zalmay Khalilzad and Taliban representatives in Doha this week as the violence has escalated.
In its latest report to the Congress on Friday, the Pentagon said a significant deterioration of security conditions in Afghanistan, however, may adversely affect the ability of India to provide aid to the war-torn country.
"This is a very difficult time. With everything going on in Iran and all the provocations and counteractions, and to have no Secretary of Defence at this time is appalling," said Democratic Sen Chuck Schumer of New York.