Vladimir Putin has warned Russia's enemies they will 'be served with poison' as police revealed a Russian spy and his daughter were 'targeted specifically' with nerve agent.

The Russian president also said Western sanctions for Moscow's annexation of Crimea in the Ukraine were 'illegitimate and unfair'.

He continued: 'Those who serve us with poison will eventually swallow it and poison themselves.'

Putin made his comments as Scotland Yard continue their investigation into the poisoning of Sergei Skripal, 66, and his daughter Yulia, 33, who are critically ill in hospital after being exposed to a nerve agent in Salisbury.

Russia´s President Vladimir Putin smiles while speaking during his visit to the Samara bakery

Sergei Skripal (left, in 2006) and his daughter Yulia (right) continue to fight for their lives after they were 'targeted' with a deadly substance in the middle of Salisbury town centre

Assistant Commissioner Mark Rowley, the head of counter-terrorism policing, said the incident was being treated as attempted murder and the pair had been 'targeted specifically'.

Mr Rowley also revealed that a police officer who was the first on the scene and found the pair slumped on a bench is also in a 'very serious' condition.

He declined to specify the nerve agent or how it was administered.

Assistant Commissioner Mark Rowley (right) and Chief Medical Officer Dame Sally Davies give a statement

Speaking in an interview with the Russian state television, Mr Putin lavished US President Donald Trump with praise, describing him as a great communicator.

'I have no disappointment at all,' Mr Putin said when asked about the US president.

'Moreover, on a personal level he made a very good impression on me.'

The two leaders met on the sidelines of international summits last year.

Mr Putin praised Mr Trump as a 'balanced' man, who easily gets into the gist of various issues and listens to his interlocutor.

'It's possible to negotiate with him, to search for compromises,' Mr Putin added.

Police seen putting on protective suits and gas masks in preparation to carry out further investigation work, in Salisbury

He also noted that he spent some time talking to Melania Trump when he sat next to her during an official dinner at the G20 summit in Hamburg, Germany in July.

The Russian leader said he told her and the wife of the Italian premier 'about Siberia and Kamchatka, about fishing … about bears on Kamchatka and tigers in the Far East'.

'I made some exaggerations,' the action-loving Russian leader said with a grin.

'When you talk about fishing, you can't help exaggerating.'

He also noted that he spent some time talking to Melania Trump when he sat next to her during an official dinner at the G20 summit in Hamburg, Germany in July

Asked if he was trying to recruit the women, the KGB veteran responded by saying: 'No, I stopped dealing with that a long time ago.'

He added with a smile: 'But I liked doing that, it was my job for many years.'

Venting his frustration with the US political system, Mr Putin said: 'It has demonstrated its inefficiency and has been eating itself up.'

'It's quite difficult to interact with such a system, because it's unpredictable,' Mr Putin said.

Moscow's hopes for better ties with Washington have been dashed by the ongoing congressional and FBI investigations into allegations of collusion between Mr Trump's campaign and Russia.

Yulia Skripal is understood to be a businesswoman who has worked for Nike and Pepsico

Police still want to question a couple that were caught near the scene on CCTV, who were initially believed to be Mr Skripal and his 33-year-old daughter

Speaking about the bitter tensions in Russia-West relations, Mr Putin said they have been rooted in Western efforts to contain and weaken Russia.

'We are a great power, and no one likes competition,' he said.

He said he was particularly dismayed by what he described as the US role in the ousting of Ukraine's Russia-friendly president in February 2014 amid massive protests.

Mr Putin charged that the US had asked Russia to help persuade then-President Viktor Yanukovych not to use force against protesters and then 'rudely and blatantly' cheated Russia, sponsoring what he described as a 'coup'.

Responding to a question about Russia's growing global leverage, Mr Putin responded: 'If we play strongly with weak cards, it means the others are just poor players, they aren't as strong as it seemed, they must be lacking something.'

Mr Putin, who presented a sweeping array of new Russian nuclear weapons last week, voiced hope that nuclear weapons will never be used but warned that Russia will retaliate in kind if it comes under a nuclear attack.

'The decision to use nuclear weapons can only be made if our early warning system not only detects a missile launch but clearly forecasts its flight path and the time when warheads reach the Russian territory,' he said.

'If someone makes a decision to destroy Russia, then we have a legitimate right to respond.'

He added starkly: 'Yes, it will mean a global catastrophe for mankind, for the entire world. But as a citizen of Russia and the head of Russian state I would ask: What is such a world for, if there were no Russia?'