US Secretary of State Colin Powell promised in a letter to his Chinese counterpart Li Zhaoxing that the United States government would thoroughly investigate the beating case of a Chinese citizen Zhao Yan according to US laws.

In a letter that Chinese Foreign Minister Li Zhaoxing received Thursday, Powell said he felt deeply disturbed when he learned of the mistreatment that Chinese citizen Zhao Yan underwent at the hands of US Customs and Border Protection officers.

Powell said that the accused officer has been suspended from his post and detained on charges of felony assault, pledging that the US government would continue its thorough investigation.

Zhao Yan, a Chinese business woman from Tianjin, was on her first US business trip when she was attacked at Niagara Falls near the US-Canadian border on July 21 by US Customs and Border Protection police. The attack came in disregard of all normal procedures.

Zhao said she had a broken tooth and severe back pain, which forced her to ride in a wheelchair. Because of sharp physical pain and mental trauma caused by the beating, she could "barely sleep two to three hours a day."

Zhao's experience has drawn much attention from the Chinese government and media. Chinese Foreign Minister Li Zhaoxing on Monday urged the US government through a telephone conversation with Powell to carry out a thorough investigation into the attack.

Those responsible for the incident should receive legal punishment, Li said.