The Obama administration has delivered a warning to Beijing about the presence of Chinese government agents operating secretly in the United States to pressure prominent expatriates–some wanted in China on charges of corruption–to return home immediately, according to American officials.

On Sunday, the U.S. government made a regrettable move by ordering the Chinese law enforcement personnel in the country for the "Fox Hunt" operation to return home immediately. Regrettable is such action as China's operation is legitimate and has been approved in bilateral agreements reached earlier this year.

The Obama administration has warned China about the use of undercover operatives in the United States who are assigned to pressure Chinese fugitives to return home and in some cases to recover assets gained through alleged corruption, U.S. officials said.

Mr. Ling is now the focus of political intrigue that could overshadow a visit to the U.S. in September by China's leader, Xi Jinping. Diplomats and analysts said Mr. Ling might have had access through this brother to sensitive information about Chinese leaders.