The United States Justice Department has in recent months escalated its antitrust probe on Apple Inc., The Wall Street Journal reported on Wednesday citing people familiar with the matter.

Reuters had previously reported the Justice Department opened an antitrust probe into Apple in 2019.

The Wall Street Journal report said more litigators have now been assigned, while new requests for documents and consultations have been made with all the companies involved.

The probe will also look at whether Apple's mobile operating system, iOS, is anti-competitive, favoring its own products over those of outside developers, the report added.

The Justice Department declined to comment, while Apple did not immediately respond to a request for comment. (Reuters via VOA)