All four parties in Germany's lower house, the Bundestag, agreed last month to launch the inquiry into the scope of spying on Germans' communications by the US and its allies, including the alleged monitoring of Chancellor Angela Merkel's cellphone.
Opposition lawmakers said Snowden would be a key witness, despite the difficulties of seeking testimony. But panel chairman Clemens Binninger, a member of Merkel's party, said he was skeptical about whether Snowden could help.