The U.S. government assisted in downloading the voice recorder of the crashed China Eastern Airlines plane and sent an investigation team to China

The U.S. federal government's independent investigative agency, the National Transportation Safety Board (NTSB), said Friday it was in Washington assisting Chinese investigators in downloading the cockpit voice recorder of the Boeing 737-800 crashed by China Eastern Airlines, while also sending an investigation team to China.

The NTSB told Reuters it helped the Civil Aviation Administration of China "download the cockpit voice recorder of China Eastern Airlines Flight 5735 at our laboratory in Washington."

China's decision to hand over a key piece of evidence to Washington for aid shows the urgency of the investigation at a time when relations between the two countries have been strained over a range of issues.

Earlier Friday, the NTSB said a team of three investigators had traveled to China to assist in the investigation. "Investigators will limit interaction with persons outside the investigation, similar to the Beijing Olympics security procedures, which will allow them to begin work immediately without quarantine," the NTSB said.

An NTSB spokesman said the U.S. team would travel to China on a commercial flight. It is unclear if they will travel to the crash site or how long they will be in China, but it is possible that they will be in China for a few weeks.

The NTSB also said a team from Boeing was also traveling to China to assist in the investigation.

Under international agreement, the NTSB has the right to participate in the investigation because the plane was designed and built in the United States.

Chinese state media reported that Chinese leader Xi Jinping chaired a meeting of the Politburo Standing Committee on Thursday, which called for "the cause and nature of the accident to be identified as soon as possible."