In an uproarious trip to Europe, Trump has harangued members of the NATO military alliance, scolded Germany for its dependence on Russian energy and shocked Britain by publicly criticising Prime Minister Theresa May's Brexit strategy.

Trump apologised to May for the furore over his withering public critique, blaming "fake news" and promising instead a bilateral trade agreement with Britain after it leaves the European Union in March.

While Trump took tea with Queen Elizabeth, a US federal grand jury charged 12 Russian intelligence officers with stealing data from the campaign of Democratic presidential candidate Hillary Clinton.

Trump has repeatedly said the investigation into suspected Russian interference in the 2016 US election - which he casts as a "rigged witch hunt" - makes it hard for him to do substantive deals with Moscow.

After meeting the Queen at Windsor Castle on Friday, Trump headed to Scotland, where his mother, Mary Anne, was born and where he owns a golf course, before his Monday meeting in Helsinki with Putin.

While at his Turnberry course on Friday evening, a powered parachute bearing the logo of environmental campaign group Greenpeace swooped within a few hundred metres of the president as he stood outside the golf course's hotel.

Trump moved calmly inside as the parachute approached, surrounded by his security detail. British police said they were trying to trace the pilot.

Protests against Trump are planned in Scotland and London on Saturday, while some supporters of Trump will also march.

Trump and Putin, who control the world's two biggest nuclear arsenals, are due to meet in the Finnish capital, a venue that evokes memories of Cold War showdowns between the Soviet Union and the US.

Trump, a 72-year-old former New York real estate developer who praises his own dealmaking skills, and Putin, a 65-year-old former KGB spy and judo black belt, are due to have some time alone at the summit.

In the most detailed US accusation to date that Moscow meddled in the presidential election, a federal grand jury said Russia's military intelligence agency officers covertly monitored computers of Clinton's campaign and Democratic campaign committees, and stole large amounts of data.

The charges put an even greater spotlight on Trump's treatment of Putin, who has repeatedly denied that Russia sought to intervene or skew the US election that Trump, a Republican, unexpectedly won.

Trump has said he plans to raise the issue. When asked at a news conference in Britain on Friday whether he would tell Putin to stay out of US elections, Trump said "yes."

The White House said the release of the charges would not affect the summit.

Australian Associated Press