Often described as the most prestigious award in the world, the Nobel Peace Prize risks losing some of its lustre because of the prize committee's unexpected and controversial choices of late, some observers warn.

The European Union, which will pick up the 2012 prize at a formal ceremony in Oslo on Monday, is the latest in a string of such laureates.

"Farce", "scandal", "joke", "ridiculous" and "absurd": those are a few of the terms detractors have used to brand the Norwegian Nobel Committee's picks in recent years, mixed in with the usual praise heaped on Oslo.

"Some of the recent choices have tarnished the reputation of the award and cast doubt on the legitimacy of the Norwegian Nobel Committee," a US journalist and expert on the prize, Scott London, told AFP.

"The peace prize is no stranger to controversy ... but I think the blunders and bad choices have become more common in recent years," he added.

After the bombshell announcement that US President Barack Obama was to win the 2009 prize in his first year in office, the prize committee this year raised eyebrows again by giving the nod to a crisis-ridden European Union plagued by divisions.

The choice prompted some unexpected swipes, including from previous laureates.

In between those two jaw-dropping laureates came the 2010 winner, jailed Chinese dissident Liu Xiaobo, who was generally hailed with the exception of Beijing which called the committee "clowns".

But the 2011 edition, which honoured three women, also courted controversy, with laureate Liberian activist Leymah Gbowee accusing her co-laureate, Liberian President Ellen Johnson Sirleaf, of corruption and nepotism.

For Norwegian lawyer Fredrik Heffermehl, author of the book "The Nobel Peace Prize: What Nobel Really Wanted" and a relentless critic of the committee, the damage has been done.

"The prize doesn't go to those who work for a global peace order made up of demilitarised nations, and it has lost its credibility, both legally and morally, by obstructing and sabotaging for years that which Nobel stood for," he told AFP.

Much of the criticism about the peace prize is aimed at the prize committee's chairman, Thorbjoern Jagland.

Since his arrival in 2009, he is believed to have influenced the four other members of the committee, with the help of its longstanding secretary, Geir Lundestad, who does not have the right to vote but whose voice carries much weight.

By straying from the instructions outlined in the 1895 will of Swedish philanthropist and inventor Alfred Nobel that created the prize, "they have in reality stolen the prize", Heffermehl claimed.

So is the Nobel discredited?

"The prize? Probably not," responded Antoine Jacob, the author of a book on the history of the Nobel prizes.

"It's still highly-awaited each year and is well-anchored in a tradition that has had its highs and survived its lows," he said.

"That said, the credibility of the committee ... has eroded since 2009 in the eyes of those who follow world affairs closely," he explained.

Jagland "wants to use the prize as a tool for his personal convictions, because he is deeply convinced that he is in the right", Jacob said.

Some have called for a reform of the committee, whose members are usually former politicians designated by the Norwegian parliament.

Among the proposals have been to open the committee to less political figures -- to further increase its independence -- and to include people more specialised in foreign affairs, possibly even foreigners.

The head of the Peace Research Institute of Oslo, Kristian Berg Harpviken, said he favoured such a reform even though he is not concerned about the Nobel's prestige.

"The controversial choices are not what threatens the status of the Nobel Prize the most. The threat comes from the consensual prizes, the rather boring ones," he said.

"The Nobel Peace Prize is so well-anchored as the most prestigious prize in the world that it can survive a good dose of controversy," he said.