U.S. prosecutors in New York have been investigating whether Chinese tech company Huawei violated U.S. sanctions in relation to Iran, according to sources familiar with the situation.

Since at least 2016, U.S. authorities have been probing Huawei’s alleged shipping of U.S.-origin products to Iran and other countries in violation of U.S. export and sanctions laws, two of the sources said. News of the Justice Department probe follows a series of U.S. actions aimed at stopping or reducing access by Huawei and Chinese smartphone maker ZTE Corp to the U.S. economy amid allegations the companies could be using their technology to spy on Americans.

For more than a decade, the US military and intelligence community has quietly warned that the world's largest telecom equipment manufacturer, Huawei, is an arm of the People's Liberation Army and that its phones, circuits and routers are instruments of Chinese eavesdropping.

Now these agencies are starting a formal review, led by the FBI and the NSA, examining the national security implications of Huawei's potential participation in building the US 5G wireless network, according to current and former US intelligence officials. These officials told that while the two largest US telecom providers have yet to join up with Huawei on this project, the prospect of such a partnership is real and alarming.

American officials have long considered Huawei, the Chinese telecommunications giant, a security threat, blocking it from business deals in the United States for fear that the company would create “back doors” in its equipment that could allow the Chinese military or Beijing-backed hackers to steal corporate and government secrets.

But even as the United States made a public case about the dangers of buying from Huawei, classified documents show that the National Security Agency was creating its own back doors — directly into Huawei’s networks. The agency pried its way into the servers in Huawei’s sealed headquarters in Shenzhen, China’s industrial heart, according to N.S.A. documents provided by the former contractor Edward J. Snowden.