Executives from two Chinese top makers of telecommunications gear denied putting hidden spy code into their equipment at a rare public hearing of the US House of Representatives Intelligence Committee on Thursday.
The officials from Huawei Technologies Co Ltd and ZTE Corp, rejecting fears that their expansion in the United States poses a security risk, said they operated independently of the Chinese government.
The congressional panel is wrapping up a nearly year-long investigation into whether the companies' equipment provides an opportunity for greater foreign espionage and threatens critical US infrastructure.
"We have heard reports about back doors or unexplained beaconing from the equipment sold by both companies," Committee Chairman Mike Rogers, a Michigan Republican, said in his opening statement.
The committee's report could be followed with proposed measures to exclude their products from the US market if determined to be security threats.
The companies, for their part, say they are frustrated by the obstacles such allegations pose to their US business.
"Huawei has not and will not jeopardize our global commercial success nor the integrity of our customers' networks for any third party, government or otherwise," Senior Vice President Charles Ding said in written testimony.
Huawei and ZTE are fighting an uphill battle for inroads into the United States, stymied by mounting government concerns about "economic espionage" attributed to China.
ZTE said sales of infrastructure equipment in the United States accounted for less than US$30 million in revenue last year, compared with a combined total of US$14 billion by two Western competitors.
Based in southern Shenzhen City, Huawei, owned by its employees, is the world's second-biggest telecommunications gear maker after Sweden's Ericsson. ZTE ranks fifth.
"What they have been calling back doors are actually software bugs," Zhu Jinyun, ZTE's senior vice president for North America and Europe, said, adding such glitches are not unlike those that require regular software patches from firms like Microsoft, Google and Apple.
Ding complained Huawei's business efforts in the United States had been hindered by "unsubstantiated, non-specific" security concerns.