A mock invasion of Sweden and Norway has been carried out by 33,000 Russian troops, a US security think tank has claimed.

Tens of thousands of soldiers rehearsed a military takeover of Swedish and Norwegian territory near the Baltic Sea in March, security expert Edward Lucas said in a report for the US-based Center for European Policy Analysis (CEPA).

The exercise also simulated the invasion of other areas including the Danish island of Bornholm, Finland's Swedish-speaking Åland islands, and northern Norway, according to the report, The Coming Storm.

Invasion: Zubr-class hovercraft, deploying marines during Russia's rehearsals for occupying part of the Baltic states

'The scenario included the speedy seizure of northern Norway, the Åland islands, the Swedish island of Gotland and the Danish island of Bornholm,' the report states.

'If carried out successfully, control of those territories would make it all but impossible for NATO allies to reinforce the Baltic states.'

Neither the Swedish Armed Forces or Norwegian defense minister wanted to comment on the report, although it was reported there were concerns in The Local.

Rehearsals: Tens of thousands of Russian soldiers are said to have rehearsed an invasion Scandinavia, two months before they were pictured here at of The Victory Day celebrations in May

Quick access: The report says that Russia could launch an attack on the Baltic's with such speed that NATO would have no time to react

A poll showed one in three Swedes think the country should join NATO, largely attributed to perceived Russian aggression, while Norwegian defence minister Ine Eriksen Søreide said the Russian exercises had changed in character.

The report went on: 'The central message of this report is that if the region's security is not improved, Nato, the world's most successful military alliance, could be revealed as powerless, perhaps without even a shot being fired.'

Lucas warned that Russia has economic interests in the Arctic, which was especially threatening to Norway.

He also does not entirely rule out the possibility of Russia invading the region.

'It is possible, though unlikely, that Russia is indeed planning a surprise full-scale military attack on the Baltic states, their Nordic neighbors and Poland,' he writes, although he concedes that doing so would mean moving troops from the borders of Eastern Ukraine.

On the move: Russian military personnel sit atop armored vehicles outside Kamensk-Shakhtinsky, Rostov Region, Russia

Military show:A mock invasion of Sweden and Norway has been carried out by 33,000 Russian troops, a US security think tank has claimed

He warned that if it did happen, NATO would be in a difficult position.

'An operation in the Baltic sea region (for example, seizing the Swedish island of Gotland) could be mounted rapidly and effectively.

'It would also be possible to invade one of the Baltic states and reach the coast within a matter of a few hours.'

This would allow Russian forces to secure their new conquests before NATO has a chance to react.

Sweden's security service Säpo recently said that its biggest intelligence threat came from Russia. Last month, the country launched a military exercise, involving a number of NATO states, held in Sweden.