The examinations come after investigators found clear similarities between the Ethiopian Airlines and Lion Air Max 8 crashes in March and October respectively.
Federal prosecutors and the US Department of Transportation are scrutinising the development of Boeing Co's 737 MAX jetliners in the wake of two deadly crashes in five months, two people briefed on the matter confirmed late on Monday.
The justice department was looking at the Federal Aviation Administration's (FAA) oversight of Boeing, one of the people said.
A federal grand jury in Washington, DC last week issued at least one subpoena to an entity involved in the plane's development, the source confirmed.
Separately, the US Department of Transportation's inspector general was also scrutinising the FAA's oversight of Boeing and the development of the 737 MAX, according to a person with knowledge of the matter who spoke on condition of anonymity.
The Wall Street Journal first reported on the justice department probe on Sunday and also said the Transportation Department's inspector general was reviewing the issue.
A Reuters source said the inspector general was believed to be involved in the matter but it was not clear whether they are assisting the justice department or planning to launch a formal investigation.
The Ethiopian Airlines disaster eight days ago killed 157 people, led to the grounding of Boeing's marquee MAX fleet globally and sparked a high-stakes inquiry for the aviation industry.