The traffic to some highly sensitive US websites was briefly rerouted via China, the US government has said.
The incident, which happened for 18 minutes last April, is published in a report by the US-China Economic and Security review commission.
It found that China Telecom sent incorrect routing information, but it is not clear whether it was intentional.
It comes amid continuing discussions in the US and the UK about cyber-security.
Among traffic rerouted via China was that destined for the websites of the US Senate, the Office of the Secretary of Defence, Nasa and the Commerce Department, the report said.
"Evidence related to this incident does not clearly indicate whether it was perpetrated intentionally and, if so, to what ends," according to the report.
"However, computer security researchers have noted that the capability could enable severe malicious activities," it added.
The danger of cyber-attacks has been high on global agendas recently.
This week, US Defence Secretary Robert Gates warned that cyber-attacks posed a huge future threat and urged more joined-up efforts between the US military and civilian agencies.
MPs in the UK have also been hearing about the risks of cyber-attacks.
In evidence given to the Science and Technology Committee, experts said that a concerted cyber-attack capable of damaging key infrastructure could currently only be launched by an enemy state.
BBC News
