The U.S. Department of Justice is investigating if Chinese tech company Huawei violated U.S. sanctions in relation to Iran, the Wall Street Journal reported on Wednesday.

It was uncertain as to how far the department's criminal probe had advanced and what allegations the federal agents were exploring, the Journal said, citing unnamed people familiar with the matter.

The Department of Justice declined comment. Huawei was not immediately available for comment.

U.S. authorities last week banned American companies from selling to Chinese smartphone maker ZTE Corp. for seven years, saying the Chinese company had broken a settlement agreement related to Iran sanctions with repeated false statements — a move that threatens to cut off ZTE's supply chain.

The ZTE ban was the result of ZTE's failure to comply with an agreement with the U.S. Commerce Department reached last year after it pleaded guilty in federal court to conspiring to violate U.S. sanctions by illegally shipping U.S. goods and technology to Iran.

In 2016, the Commerce Department made documents public that showed ZTE's misconduct and also revealed how a second company, identified only as F7, had successfully evaded U.S. export controls.

Ten lawmakers in a 2016 letter to the Commerce Department said they believed F7 to be Huawei, citing media reports.

In April 2017, lawmakers sent another letter to Commerce Secretary Wilbur Ross asking for F7 to be publicly identified and fully investigated.