Russian forces could reach the outskirts of the Baltic capitals in less than 60 hours because Nato lacks the forces to defend its eastern-most members, new analysis has shown.

According to several war games scenarios conducted by a US think-tank, it would take between 36 and 60 hours for Russian battalions to occupy the Estonian and Latvian capitals of Tallinn and Riga.

It highlights, the report says, how ineffective Nato's forces have become, as they would be entirely under-prepared for any potential attack launched by Moscow.

The report comes amid rapidly declining relations between Putin and the West.

This week, it emerged Sweden has re-militarised an old Cold War frontier base on the island of Gotland, in response to what it believes to be a rising threat from Russia, the BBC reports.

Sweden's Supreme Commander, General Micael Byden, said: "This is one of the great challenges right now: What are they up to, and why do they do it?"

The analysis by the army research division of the Rand Corporation predicted Russia would most likely launch a two-pronged assault across the Latvian border, sending heavily-armed battalions in a pincer movement towards Riga, fighting Latvian and Nato battalions along the way.

NATO sets up battle supply points in Baltics and eastern Europe

Once Latvia was secured, the remainder of Russia's 27 manoeuvre battalions would cross into Estonia to take the ethnic Russian north-East, before heading to Tallinn.

The 16-page analysis, carried out between 2014 and 2015, warns even a combination of US and Baltic troops with US air support would do little to stop Russia advancing - as Nato's ground forces are no match for Russia's battalions.

It notes Nato's 12 battalions have no battle tanks, with only one heavily armoured Stryker battalion, while all of Russia's 27 maneuver battalions have heavily-armoured battle tanks.

The report concludes: “The games’ findings are unambiguous: As currently postured, Nato cannot successfully defend the territory of its most exposed members.”

NATO reinforces Baltic presence as tensions rise with Russia

In such a scenario, Nato would be left with the options of either choosing defeat - with “predictably disastrous consequences for the Alliance and, not incidentally, the people of the Baltics" - or launching a costly counter attack, which could lead to nuclear escalation.

To defend against the Russian threat, the report suggests Nato would have to increase its deterrent force in the region.

It argues artillery and air forces supported by seven brigades, three of them heavily armoured, would be enough to deter Russia. Such a force would cost around $2.7 billion (£1.85 billion) a year.

Russia's annexation of Crimea in 2014 caused the US to start the European Reassurance Initiative, with President Obama warning Russia had taken an "aggressive posture" near Nato countries.

The Initiative commits "a persistent US air, land and sea presence in the region, especially in Central and Eastern Europe" for allies "now deeply concerned by Russia's occupation an dattempted annexation of Crimea and other provocative actions in Ukraine".