Trump, May Discuss Russia, Iran, 'Very Strong' U.S.-U.K. Relationship

British Prime Minister Theresa May poses for a photograph with U.S. President Donald Trump at Chequers in the U.K.

U.S. President Donald Trump says he has urged Britain to maintain pressure on Iran and agreed with Prime Minister Theresa May that Tehran must never possess nuclear weapons.

Trump and May spoke at a joint news conference after talks at the British prime minister's official country residence, Chequers, on July 13. Meanwhile, tens of thousands of protesters demonstrated in London against Trump.

May said that she and Trump discussed what more could be done on Iran.

They also discussed Russia, among other topics, and May thanked Trump for U.S. support after the poisoning of a former Russian spy and his daughter in England in March, which her government blames on Russia. Moscow has denied any involvement in the attack.

Trump recalled that 60 intelligence officers were expelled from the Russian Embassy in Washington in response to the attack.

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Multiple Protests Against Trump Held In Britain

WATCH: Multiple Protests Against Trump Held In Britain

Trump is in Britain for a visit sandwiched between a July 11-12 NATO summit in Brussels and a summit with Russian President Vladimir Putin in Helsinki on July 16 -- his first full-fledged meeting with Putin since taking office in January 2017.

Trump said the issues he would discuss with Putin include the conflicts in Ukraine and Syria and Russia's alleged meddling in elections including the 2016 vote that put him in office.

Asked by a reporter whether he would be giving Putin the upper hand, Trump took issue with such an assessment and said that his administration has been "extremely tough" on Russia.

He also said it would be "tremendous" if the United States and Russia could make headway on nuclear nonproliferation, and that it would be "a good thing" if the United States could get along with Russia and China.

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Trump Hopeful For Better Russia Ties Ahead Of Putin Talks

WATCH: Trump Hopeful For Better Russia Ties Ahead Of Putin Talks

Trump had said earlier the U.S. relationship with Britain was "very, very strong," even though he has publicly criticized May's strategy to leave the European Union.

Following their meeting with May, Trump and his wife, Melania, met Queen Elizabeth II at Windsor Castle, her residence outside London.

Several protests have taken place across Britain on July 13, including flying a giant balloon over Parliament in London that depicted Trump as an angry diaper-wearing baby.

In an interview with The Sun newspaper, Trump also blamed London Mayor Sadiq Khan for terror attacks against the city and argued that Europe was "losing its culture" because of immigration.

With reporting by AP and Reuters