The officials also recommended but did not move to require travellers wear face coverings in airports and on planes
The IG's report is the latest of reports faulting the plane's approval, while the Justice Department has an ongoing criminal investigation
The US planemaker and FAA said last month they were reviewing a wiring issue that could potentially cause a short circuit on the grounded 737 MAX
The warning is a part of a US Federal Aviation Administration's (FAA's) notice to airmen (NOTAM) on December 30, in which it has also flagged risks involved in operating flights in Pakistan airspace
"Exercise caution during flight operations. There is a risk to US civil aviation operating in the territory and airspace of Pakistan due to extremist/militant activity," said the US FAA
A Lion Air Boeing 737 MAX 8 crashed on Oct. 29 minutes after taking off from Jakarta, killing all 189 people aboard