Some 10 armoured combat vehicles and dozens of armed personnel could be seen patrolling the small port town of Visby on the strategically-located island.

The move came after three Russian landing ships sailed into the Baltic Sea through the Great Belt Strait in Denmark this week, and amid increased tensions between Russia and NATO.

"The armed forces are taking the necessary measures to safeguard Sweden's integrity and to demonstrate our ability to protect Sweden and Swedish interests", Defence Minister Peter Hultqvist told AFP in emailed remarks.

In a statement late Thursday, the military said troops would be deployed "to reinforce operations in multiple locations" due to "increased Russian activity in the Baltic Sea".

Sweden has flexed its military muscle in the past during exercises, but rarely as a direct response to current events.

Hultqvist also told news agency TT the increased patrols on Gotland showed Sweden was taking the situation seriously and would "not be caught off-guard."

"We are not unaware of the security risks that exist."

Swedish Armed Forces chief of operations, Michael Claesson, told AFP the units deployed to Visby were from the garrison already stationed on the island, denying it was a "show a force."

"This doesn't have to been seen as particularly dramatic, but this is a natural way of adapting the military presence," Claesson told AFP.

Western powers have accused Russia of deploying tanks, artillery and about 100,000 soldiers on Ukraine's war-torn eastern border in recent weeks, in what NATO says is preparation for an invasion.

Moscow says this is a response to what it sees as the growing presence of NATO in its sphere of influence, where it fiercely opposes the expansion of the Atlantic alliance.

Sweden is not a NATO member, but does cooperate closely with the alliance. Russia recently warned of "grave consequences" if the Scandinavian country were to join.

After the end of the Cold War, Stockholm slashed its military spending. But following Russia's annexation of the Crimean Peninsula in 2014, it has reversed course and bolstered its defences.

Sweden, which has not been to war in two centuries, reintroduced mandatory military service in 2017 and reopened its garrison on Gotland in January 2018 amid concerns about Russian intentions in Europe.