Vladimir Putin will employ flattery to manipulate "sociopathic narcissist" Donald Trump, former spies have predicted ahead of the two leaders' much-anticipated first meeting

The two presidents will come face to face for the first time at the G20 summit on Friday afternoon, against a backdrop of allegations that Russia interfered in last year's US election.

It comes a day after Mr Trump ramped up political tensions by accusing Russia of "destabilising" Ukraine and supporting hostile regimes.

But veteran spies who have studied manipulation tactics predicted Mr Putin would have the upper hand in their high-stakes meeting in Hamburg and would exploit his American counterpart's ego to his own advantage.

“Trump is just about a sociopathic narcissist,” Glenn Carle, a retired CIA interrogator and analyst, told the Daily Beast.

He added: “Fulsome praise, full of garbage, is a small price to pay to get what you want.”

Naveed Jamali, a former undercover FBI double agent, said: "The truly scary part is Putin only has to say to Trump ‘You are right and the haters are wrong’ to manipulate him."

The Polish government bussed people into Warsaw on Thursday to ensure a large and friendly crowd for a speech by Mr Trump, who smiled as spectators chanted his name during the address.

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He later tweeted: "Thank you to everyone, including the haters, for the great reviews of the speech!"

Speaking in Krasinski Square, Mr Trump stopped short of condemning Moscow for meddling in the US presidential election and refused to say whether he would raise the issue when the leaders meet behind closed doors.

But he sought to demonstrate that he was not overlooking Russian acts that have sparked global concern, especially from Poland and other eastern and central European nations.

"We urge Russia to cease its destabilising activities in Ukraine and elsewhere, and its support for hostile regimes including Syria and Iran, and to join the community of responsible nations in our fight against common enemies and in defence of civilisation itself," he said.

His criticism of Russia did not extend to its actions during last year's presidential campaign. Multiple US intelligence agencies have concluded Russia meddled in the election to benefit Mr Trump, who has refused to embrace the finding wholeheartedly.

As investigations into Russian interference continue, the US President is under intense scrutiny over how he handles his first meeting with Mr Putin, a former KGB agent.

A group of senior Democratic US senators on Thursday said Mr Trump would be in "severe dereliction" of his presidential duty if he fails to confront his Russian counterpart.

During a news conference before his Warsaw speech, Mr Trump questioned the reliability of US intelligence and argued Russia was not the only country that might be guilty of interfering.

"Nobody really knows for sure," he said.

Syria, North Korea and Ukraine are all expected to be on the agenda as the two presidents meet, with ex-spies predicting Mr Putin would look to influence US policy.