An unusually high amount of suspicious phone activity in Washington, D.C. is fueling reports that a cell network in the city may have been hacked and communications may be being monitored, according to the Washington Free Beacon.

Documents reviewed by the paper suggest that hackers have stolen a considerable amount of data from the cellular communications in the region, including from U.S. government officials and foreign diplomats. A cybersecurity expert has reportedly confirmed the suspicious activity to members of Congress and pinpointed T-Mobile’s network as being compromised.

T-Mobile declined to comment.

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The activity was flagged by the Department of Homeland Security (DHS) and confirmed to CBS by telecommunications security firm ESD America, which is working been working on a pilot program with DHS since January.

The 90-day initiative, known as ESD Overwatch, was launched in the final days of the Barack Obama administration and was designed to monitor cell towers for suspicious behavior and anomalies.

It has reportedly identified a number of spikes in activity in other parts of the country, though the oddities began in the D.C. area, with sensors near the White House and Pentagon identifying suspicious behavior.

The activity points to the possibility that large numbers of calls and communications are being tracked. The hack could also allow for an attacker to clone phone numbers and spread malware.

Reports have indicated based on the type of technology used, it is believed the activity was being conducted by a foreign nation.

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Democratic congressman Ted Lieu of California confirmed to BuzzFeed that his office received notification from a cybersecurity last week that T-Mobile’s network in the D.C. area may have been compromised by an attack.

Representative Lieu and Democratic Senator Ron Wyden of Oregon wrote a letter to Homeland Security Secretary John Kelly earlier this week, requesting details on what resources have been directed at protecting against attacks on cell networks.