Cisco Systems Inc., the largest maker of networking equipment, ended a partnership with ZTE Corp. amid concerns over the Chinese company’s alleged sale of equipment to an Iranian company.

ZTE, along with Huawei Technologies Co., provides opportunities for Chinese intelligence services to tamper with U.S. telecommunications networks for spying, according to a U.S. congressional report released today. ZTE refused to answer questions about its interactions with China’s government, as well as questions concerning sales in Iran and other countries that are targets of U.S. sanctions, according to the report.

ZTE sold to an Iranian telecommunications company a surveillance system capable of monitoring landline, mobile and Internet communications, Reuters reported in March.

Shenzhen-based ZTE had been reselling Cisco products as part of a partnership between the two companies. ZTE’s sales to Iran had included Cisco switches, according to Reuters.

Margrete Ma, a spokeswoman for ZTE, didn’t immediately respond to requests for comment left outside regular business hours. Zhu Jinyun, ZTE’s senior vice president for North America and Europe, said at a Sept. 13 congressional hearing that the company conducts “normal business operations in Iran” and is “gradually reducing our present operations and we are not starting any new business operations in Iran.”

Zhu also said that the company hasn’t sold gear to the Iranian government.