Federal prosecutors in California are conducting a criminal probe into e-cigarette maker Juul Labs Inc., the Wall Street Journal reported on Monday, citing people familiar with the matter.

The focus of the probe by the U.S. attorney's office of the Northern District of California, which is in early stages, was unclear, the report said.

The company, in which tobacco giant Altria group owns a 35% stake, is facing a regulatory crackdown and increased government scrutiny in the domestic market as teenage use of e-cigarettes surges.

Six deaths have been linked to vaping and U.S. public health officials are investigating 450 cases of potential vaping related lung illness across 33 states and one U.S. territory.

The U.S. Food and Drug Administration earlier this month warned Juul over marketing its products as safer than traditional cigarettes and requested documents and information within 30 days from the letter.

The Trump administration announced plans earlier this month to remove all flavored e-cigarettes from store shelves in a widening crackdown on vaping.

A spokesman for the attorney's office declined to comment. Juul did not immediately respond to a Reuters request for comment.