U.S. intelligence agencies are investigating whether Edward Snowden's leaks may be a Chinese intelligence operation or whether China might have used his concerns about U.S. surveillance practices to exploit him, according to four American officials.

The officials emphasized there's no hard evidence yet that Snowden was a Chinese agent or that China helped plan his flights to Hong Kong and then to Moscow, directly or through a witting or unwitting intermediary. Rather, they are duty-bound to probe such a worst-case scenario for the U.S., said the officials, who are familiar with the case and asked not to be identified to discuss classified intelligence.

President Barack Obama said the U.S. is working with other nations to gain custody of Snowden on espionage charges, as administration officials chastised China for letting him leave Hong Kong for Moscow and pressed Russia to turn him over on the assumption that he's still there.