Russian diplomats may be a front for Putin's spies lining up "acts of sabotage" on targets across Europe as part of a plan to weaken the West, EU and Nato chiefs have warned.
Eight European countries - the Czech Republic, Denmark, Estonia, Latvia, Lithuania, the Netherlands, Poland and Romania - have written to EU security boss Josep Borrell to call for a bloc-wide crackdown on free movement for Russian diplomatic or service passport-holders to ward off the threat of "malign activities".
In the letter, the states raised fears that the EU and Schengen Area's freedom of movement allowance may essentially be leaving open a backdoor for the "preparation of sabotage acts", which they claimed are "the main workload for a large number of Russian 'diplomats' in the EU".
The letter read: "Free movement of holders of Russian diplomatic and service passports, accredited in one host state, across the whole Schengen area, is easing malign activities."
It added that any crackdown should "restrict the movement of members of Russian diplomatic missions and their family members to territory of a state of their accreditation only", and hand authorities to detain and chuck out those found outside their allocated area.
The letter said this measure would "significantly narrow operational space for Russian agents", while a senior diplomat added: "The EU is a soft touch and open door for Russian operatives using diplomatic cover... It has to stop."
At the same time, Nato chief Jens Stoltenberg hailed the onset of his own bloc's crackdown on Russian operatives in Europe after a spate of attacks targeted the UK and key Western allies including Germany and Poland.
Stoltenberg said the alliance had seen several examples of Russian sabotage, arson, cyber attacks and disinformation, with the number of incidents only increasing over the past weeks and months.
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He said Nato saw a pattern evolving and that the attacks were a result of Russian intelligence being more active across the alliance.
At the end of May, Polish security services arrested a man suspected of trying to obtain photos of military vehicles crossing the border into Ukraine, as well as three men accused of committing arson on the orders of Russian intelligence.
Around the same time, the German military reported the discovery of explosives attached to a Nato pipeline running through the country.
And the alliance's defence ministers are set to meet in Brussels in a landmark summit in the coming days - with Russia the key focus.
Delegates are set to discuss options for how to respond to the "Russian campaign of hostile activities against Nato allies", Stoltenberg added, including the protection of critical maritime and cyber infrastructure, as well as "tighter restrictions on Russian intelligence personnel across the alliance".
At a time of rising tensions with Russia, Nato countries have publicly booted out hundreds of alleged spies - with Moscow taking reciprocal action against Western officials.
Nato has also expelled what it called "undeclared Russian intelligence officers" who had been working at Moscow's mission to the alliance in Brussels last month.
And just last month, authorities swooped on EU buildings following reports that MEPs had been paid to promote Russian propaganda via the "Voice of Europe" news site.