BEIJING, Jan. 10 (Xinhua) -- Mice discovered on a United Airlines (UA) flight from Washington D.C. over the weekend were virus-free, China's quality watchdog said on Thursday.

    Flight UA897, which connects the two capitals, got the green light to return to service as soon as test results were available, said an official of the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ).

    At least eight dead and live mice were found on the plane, after UA reported Sunday afternoon upon landing that they found live mice on the plane. The report prompted Chinese authorities to test the rodents for fatal viruses, such as plague spot virus or hantaan virus. The tests indicated that the animals, all small house mice of which four were male, were free of viruses or parasites, according to the AQSIQ.

    The administration said no further rodents were subsequently found on the aircraft after they put poison and traps there, and quarantine staff had taken preventive measures in the passenger cabin and cargo hold.

    The AQSIQ said it had informed UA in writing of the quarantine efforts and lab test results. All work done by the Chinese side had been carried out in the presence of UA staff and "would in no way affect the security of the plane," the agency said in the report.

    Experts said mice could spread more than 35 fatal viruses or cause serious accidents if they chewed wiring in the plane. They also commented that it was very rare to find so many mice on one aircraft.