The possibility of ex-NSA contractor Edward Snowden being brought to Berlin to give evidence before a parliamentary committee has risen after a top appeals court ruled the German government cannot block him.

The committee investigating US National Security Agency (NSA) surveillance in Germany has wanted to call Snowden as a witness to detail what he knows but the government has said it cannot guarantee his safety.

Snowden is wanted by the US on espionage charges.

But in a ruling announced on Monday, the Federal Court of Justice said the government needs to "establish the pre-conditions" including "effective protection of the witness".

The committee is now required to make an official request to bring in Snowden from Russia, a matter it is expected to debate on Thursday.

Snowden has reportedly said he is willing to give evidence, but only in person in Germany.

Head of the European Center for Constitutional and Human Rights and head of my EU legal team on German Supreme Court's surprise decision: https://t.co/b7HTxWfAkw — Edward Snowden (@Snowden) November 21, 2016

AP