Ukraine: The spy war within the war

The decades-long spy conflict between Russia and the West is intensifying over the Ukraine war. But what are Russia's intelligence services suspected of doing and how will their officials' expulsion from capitals affect Putin's clandestine overseas operations?

When Russia first targeted its military forces on Ukraine in 2014 it also unleashed its intelligence services on the West - from interfering with the US elections using cyber attacks to poisonings and sabotage in Europe.

But in recent months the spy war has intensified as Western countries have sought to hit back and inflict lasting damage on the ability of Russian intelligence to carry out covert operations. This is symbolised by the unprecedented expulsion of 500 Russian officials from Western capitals.

Formally, these officials are described as diplomats, but the majority are believed to be undercover intelligence officers. Some will have been carrying out traditional espionage - cultivating contacts and recruiting agents who can pass on secrets - something Western countries do inside Russia too.

But some were believed to be carrying out what Russians call "active measures". These range from spreading propaganda, to more aggressive covert activity. Poland said the 45 Russians it expelled were involved in actions to "undermine the stability" of the country.

Since 2014, Western intelligence agencies have been working to identify Russian spies involved in such activities. One of those is GRU Unit 29155 of Russian military intelligence, which is believed to be tasked with sabotage, subversion and assassination.