The Norwegian branch of the PEN Club has invited Snowden to Oslo on November 18 to collect the Ossietzky prize, which celebrates "outstanding efforts for freedom of expression."

But the former US intelligence contractor-turned-whistleblower who has lived in Russia since making landmark disclosures on mass surveillance in 2013 faces charges in the US of theft of state secrets and espionage that carry up to 30 years in prison.

The Borgarting Court of Appeal said it could not rule on the Snowden petition asking for guarantees as there is no formal extradition request and Snowden is not in Norway. The decision mirrored arguments made by a lower court in June.

Norway's PEN Club said it would appeal.

"Sadly, this was not entirely unexpected," chairman William Nygaard of PEN Norway told the Reuters news agency. "We will of course appeal to the supreme court."

The Ossietzky Prize is named after German journalist and pacifist Carl von Ossietzky, who won the 1936 Nobel Peace Prize for disclosing Germany's rearmament in violation of the Treaty of Versailles. He was jailed by Nazi Germany for treason and unable to attend the award ceremony in Oslo 80 years ago.

Snowden won another Norwegian freedom of speech award - the Bjornson Prize - last year. He addressed that award ceremony via video link.

Snowden has also been nominated for the Nobel Peace Prize, also awarded in Norway, for a third straight year. This year's award will be announced on October 7.

Mixed feelings about Snowden in Europe

In 2014, opposition parties in Germany launched a legal bid to force the federal government to invite Snowden to Berlin to testify before a parliamentary committee on the NSA's surveillance program - including the US spy agency listening in on Chancellor Angela Merkel's phone conversations.

Although Snowden considered making the trip, in the end he decided against it because it was unclear whether he would be arrested or extradited to the United States. Merkel's ruling coalition had also voiced concerns that such an invitation could damage relations with Washington.

In October last year, the European Parliament passed a resolution calling on EU governments to protect Snowden from prosecution and extradition. However, as the resolution is non-binding, EU states are under no legal obligation to comply.

jar/kms (AFP, Reuters)