"China has been briefed by the United States about the issue," Liu said.

"We attach importance on this issue, and are earnestly investigating it. We are making our best efforts to protect the safety of foreign organizations and their personnel," he said.

A notice posted on the US Embassy's website Friday said the US government has received unconfirmed information of a possible terrorist threat against US interests in China, especially in the cities of Beijing, Shanghai and Guangzhou.

A US Embassy spokeswoman has said the notice was specific to China, and not part of a global warning.