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WASHINGTON (Reuters) - The Democratic National Committee warned party candidates running in November elections not to use devices made by Chinese telecommunications companies ZTE Corp and Huawei Technologies because they pose a security risk, a Democratic source said on Friday.

U.S. lawmakers and the Trump administration have pressured U.S. companies to not sell Huawei or ZTE 000063.SZ products, saying they potentially could be used to spy on Americans. Earlier this year they pushed AT&T T.N to drop a deal with Huawei to sell its smartphones in the United States.

The source said Bob Lord, the DNC’s chief security officer, said in a email that it was important for party and campaign workers to be vigilant about the warnings.

“Please make sure that you are not using or purchasing ZTE or Huawei devices anywhere within your staff - for personal or work-related use,” Lord said.

Federal Communications Commission Chairman Ajit Pai told Congress in March he shared the concerns of U.S. lawmakers about espionage threats from Huawei.

“Hidden ‘back doors’ to our networks in routers, switches - and virtually any other type of telecommunications equipment - can provide an avenue for hostile governments to inject viruses, launch denial-of-service attacks, steal data, and more,” Pai said at the time.

The U.S. Department of Defense has already stopped selling mobile phones and modems made by Huawei and ZTE in stores on its military bases, citing potential security risks.