SAN FRANCISCO (Reuters) -A U.S. senator is asking the Pentagon for more information on Microsoft's reported use of Chinese engineers in maintaining military cloud computing systems, according to a copy of the letter seen by Reuters.

Senator Tom Cotton, an Arkansas Republican who chairs the chamber's intelligence committee and also serves on its armed services committee, sent the letter to Defense Secretary Pete Hegseth after a report in investigative journalism publication ProPublica earlier this week. The report detailed Microsoft's use of Chinese engineers to work on U.S. military computing systems under the supervision of U.S. "digital escorts" hired through subcontractors who have security clearances but often lacked the technical skills to assess whether the work of the Chinese engineers posed a cybersecurity threat.

Contacted by Reuters about both the ProPublica report and Cotton's letter, Microsoft declined to comment. The company, which is a major contractor to the U.S. government and whose systems have been breached by both Chinese and Russian hackers, told ProPublica that it disclosed its practices to the U.S. government during an authorization process.

The Defense Department did not immediately respond to a request for comment.

Cotton asked the U.S. military for a list of all contractors that use Chinese personnel and for more information on how U.S. "digital escorts" are trained to detect suspicious activity.

"The U.S. government recognizes that China's cyber capabilities pose one of the most aggressive and dangerous threats to the United States, as evidenced by infiltration of our critical infrastructure, telecommunications networks, and supply chains," Cotton wrote in the letter. The U.S. military "must guard against all potential threats within its supply chain, including those from subcontractors."