The offices of Montana senators Steve Daines and Jon Tester have reached out to the U.S. State Department and the U.S. and Chinese embassies after a University of Montana student was taken into police custody in China.

Guthrie McLean was arrested Sunday because of an altercation with a Chinese cab driver that occurred a month ago.

His mother, Jennifer McLean, told Montana’s senators that Guthrie is accused of assaulting the taxi driver. She said her son was actually coming to her aid after the driver attacked her during a dispute over a fare.

Police in China have refused to confirm or deny Guthrie’s imprisonment to U.S. media outlets.

Jennifer McLean teaches English in Zhengzhou, southwest of Beijing. She told CBS News that her son has been held since Sunday on bond of 50,000 Renminbi (about $7,300).

He has not yet been formally charged with any crime.

In a written statement Wednesday, Montana Sen. Jon Tester’s office said: "Senator Tester's office was informed of this incident on Monday, and within minutes contacted the State Department and the U.S. Embassy in China.  Senator Tester is working closely and urgently with officials here and abroad to secure Mr. McLean's quick release and to safely resolve this matter."

Sen. Daines' office said he has contacted the U.S. State Department, the U.S. Embassy and the Chinese Embassy. He also posted a notice about Guthrie McLean’s arrest and jailing on his Senate website.

Jennifer McLean told CBS News that U.S. State Department officials told her they may be able to visit her son on Friday.

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