Two countries on Nato’s eastern flank have warned that Russia is preparing a possible “provocation” in the Baltic states or Poland in an effort to test the cohesion of the western military alliance.

Western sources also fear there could be danger on the horizon because the Kremlin is coming under pressure from Ukraine’s campaign of long-range attacks on targets near Moscow and St Petersburg.

On Monday, Latvian intelligence said: “We see indications that Russia is preparing military provocations against the Baltic countries or Poland.” However, it would be well short of a full scale attack.

A senior political source from a second Nato member made a similar statement last week. They said “we are picking up intelligence” that Vladimir Putin was “planning something against the Baltic states”.

They said Putin might be willing to test US support for some of Nato’s smallest member countries – Estonia, Latvia and Lithuania – in a desperate effort “to throw the dice” as Russia struggles with its invasion of Ukraine.

Latvian intelligence said Russia was not capable of opening a second front, but was considering “hybrid attacks, such as missiles, drones or other actions designed to send a signal: stop supporting Ukraine, or you will have your own problems”.

Though the warnings appear linked, there was only limited supporting detail, unlike the detailed warnings released by the CIA and MI6 before Russia’s full-scale invasion of Ukraine in February 2022.

But they come at time when Russia’s advance in Ukraine has stalled, raising questions about whether the Kremlin would turn to alternative strategies to break the deadlock or change the dynamics in its favour.

Keir Giles, a Russia expert with the Chatham House thinktank, said: “Moscow will be looking for ways to disrupt the current trend, through horizontal escalation [spreading the conflict to other countries] or doing something elsewhere. We should not expect Russia to passively lose.”

Russia’s relative weakness was underlined this week when drone relay stations in Belarus stopped operating after Ukraine threatened to attack them. Volodymyr Zelenskyy, Ukraine’s president, had given Belarus a one-week warning last Friday, saying the equipment enabled Russian attacks on his country.

One Telegram channel reported that the Belarusian authorities in the Brest and Gomel regions of the country had demanded the mobile operators dismantle the repeaters because they were interfering with grouse nesting sites.

Nato will hold its annual summit in Ankara, Turkey, this month amid uncertainty about US commitment to the alliance. On Wednesday, Donald Trump said he felt “let down” by European allies who did not allow the US air force to bomb Iran from airfields in their countries.

Since the start of the full-scale invasion of Ukraine there have been several waves of Russian sabotage and provocative activity, including the planting of firebombs in DHL parcels in the UK, Poland and Germany in the summer of 2024.

Last September, 19 Russian decoy drones crossed into Polish airspace, prompting Nato to scramble jets to try to shoot them down as people in three eastern provinces were told to shelter indoors.

Ukraine has gradually developed a homegrown deep strike attack capability able to hit targets 2,000km inside Russia. Last week nearly 200 drones hit several locations in Moscow and black oil rained down on parts of the Russian capital after a refinery was bombed.

A western military source said there was a concern that Russia could lash out if Putin thought he was under pressure as the war shifted to the skylines of Moscow and St Petersburg. “I cannot lie, that is a period of danger,” they said.

Worries about a possible Russian escalation also surfaced in the autumn of 2022, when a sudden set of reversals in Kharkiv province led to western fears that Moscow could even use a nuclear weapon to protect itself. But there was no evidence of steps to an actual deployment and the frontline stabilised by the end of the year.