Snowden, the former intelligence analyst who revealed the extend of US global eavesdropping, was one of the joint winners of the "alternative Nobel peace prize" last month. A hero to some and a traitor to others, he would be a highly controversial choice for the 878,000-euro ($1.11-million) award.

The Pakistani girls' education campaigner Malala Yousafzai — who was also a favourite last year — is also said to be in the running along with Pope Francis and a Japanese pacifist group.

Predicting the winner is even harder than usual this year, as the Nobel committee has received a record 278 candidates, so experts only have the names of those made public by their sponsors to go on.

Snowden, a former National Security Agency (NSA) analyst, was proposed by two Norwegian members of parliament. Last month he shared the "alternative" $210,000 Norwegian Right Livelihood Award with The Guardian newspaper and human rights and environmental activists.

But from his exile in Russia, the US fugitive said during a recent press conference that "it is somewhat unlikely that the Nobel committee would back..." him winning the real Nobel.

However, other Russian-based individuals or groups could be a popular choice for the Nobel Committee.

"Russia's policy in Ukraine, annexing Crimea and questioning borders, but also the way the Kremlin treats dissenters cannot be ignored by the Nobel committee," said Antoine Jacob, author of a history of the Nobel prizes.

For the Nobel committee president Thorbjoern Jagland, "sanctioning Moscow would... be a way to prove that he acts independently, since (Jagland) is (also) the Secretary General of the Council of Europe, which counts Russia as a member," Jacob told AFP.

Co-founded by Mikhail Gorbachev in 1993 with part of his peace prize money, the pro-democracy Moscow newspaper Novaya Gazeta has been tipped as a possible laureate. It is one of the few independent media outlets left in Russia and has seen several of its journalists murdered, including Anna Politkovskaya who exposed huge human rights abuses in Chechnya.

- Malala 'still very young' -

Kristian Berg Harpviken, director of the Peace Research Institute Oslo (PRIO), a leading peace prize analyst and one of the few to publish a shortlist, revised his prediction in the last week, putting the peace group Japanese People Who Conserve Article 9 — which wants to maintain the Asian country's anti-war constitution — in first place ahead of Malala.

"We may have come to think of wars between states as virtually extinct after the end of the Cold War, but events in Ukraine and simmering tensions in East Asia remind us they may reappear, and a return to a principle often hailed in earlier periods of the Peace Prize would be well timed," he wrote in an online explanation of his choice.

Harpviken — who has yet to accurately predict a peace prize winner, despite his expertise — ranked Snowden and Novaya Gazeta in second and third place.

Nobeliana.com, a website run by leading Norwegian Nobel historians ranked Malala — who was shot in the head by the Taliban in 2012 — as their top candidate ahead of Snowden, for her fight for girls' right to an education around the world.

But the historians noted that, despite the issue of girls' rights being topical — with the Boko Haram mass kidnapping in Nigeria in April and the ongoing mistreatment of women by the fundamentalist Islamic State group in Syria and Iraq — there were several reasons to doubt that the committee would nominate her.

"She is still very young (17 years), and she has said that she does not deserve the Peace Prize yet. As a Nobel laureate she will be an even greater target for extremist groups," they wrote.

Other favourites, also tipped last year, were Congolese doctor Denis Mukwege who has treated female victims of sexual violence for the last 25 years, and the human rights activist Ales Bialiatski from Belarus, who was released from prison by the Russian-backed dictatorship in June.

The bookmakers Paddy Power are banking on Pope Francis for his outspoken defence of the poor, giving him 9/4 odds, far ahead of another candidate who is also believed to have been nominated — Vladimir Putin, a long shot at 50/1.