T-Mobile (TMUS) was among the multiple US and international telecommunications companies breached by hackers linked to a Chinese intelligence agency, the Wall Street Journal reported Friday, citing people familiar with the matter.

The extent of the data breach was unclear, the Journal said, adding that the attack was part of a monthslong campaign to spy on the cellphone communications of high-value intelligence targets. The timeframe of the attack was not reported.

"T-Mobile is closely monitoring this industry-wide attack, the company was quoted saying in a statement to multiple media outlets. "At this time, T-Mobile systems and data have not been impacted in any significant way, and we have no evidence of impacts to customer information," it added.

T-Mobile did not immediately respond to MT Newswires' request for comment.

In October, the Journal reported that Chinese hackers have breached the networks of telecommunications firms AT&T (T), Verizon (VZ) and Lumen Technologies (LUMN).

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