A US government security review has found no evidence telecoms equipment firm Huawei Technology spies for China.
The 18-month review, details of which were leaked to the Reuters news agency, suggests security vulnerabilities posed a greater threat than any links between the firm and the Chinese government.
Last week a US congressional report warned against allowing Chinese companies Huawei and ZTE Corp to supply critical telecom infrastructure.
The firms have always denied espionage.
The classified inquiry was a thorough review of how Huawei worked, involving nearly 1,000 telecom equipment buyers.
One of the government employees involved with the inquiry told Reuters: "We knew certain parts of government really wanted evidence of active spying. We would have found it if it were there."
Huawei spokesman Bill Plummer said: "Huawei is not familiar with the review, but we are not surprised to hear that the White House has concluded there is no evidence of any Huawei involvement with any espionage or other non-commercial activities.
"Huawei is a $32bn [£19bn] independent multinational that would not jeopardise its success or the integrity of its customers' networks for any government or third party - ever," he added.
ZTE's senior vice president of Europe and North America, Zhu Jiny, told the BBC: "The security issues should not be focused on the Chinese companies. These are problems of the world situation. It's not only Chinese companies - it's a global issue."
Last week at a conference in Malaysia, Felix Lindner, an expert in network equipment security, said he had discovered multiple vulnerabilities in Huawei's routers.
"I'd say it was five times easier to find one in a Huawei router than in a Cisco one," he said.
He blamed sloppy coding rather than any deliberate attempt to leave backdoors open for spying purposes.
Questions about the relationship between Huawei, ZTC and the Chinese government circulated last week following a report from the US House Intelligence Committee.
While the report did not present concrete evidence that either Huawei or ZTE had stolen US data, it said had classified information that provided "significantly more information adding to the committee's concerns" about the risk to the United States.
It also criticised Huawei for failing to provide details about its relationship with the Chinese government.
Attitudes about Huawei differ from nation to nation.
Canada said last week that the firm could not bid to help build a secure national network. In Britain, however, a spokesman for the Cabinet Office said Huawei's products were fully vetted and did not represent a security concern.