Prime Minister Theresa May refused to be drawn on Donald Trump's boast that he had a bigger and more powerful "nuclear button" than North Korean leader Kim Jong Un.
Mr Trump tweeted that he had a ''much bigger & more powerful'' nuclear button after Mr Kim warned "the whole territory of the US is within the range of our nuclear strike".
Mrs May, who was visiting homeowners who had benefited from stamp duty reforms in Wokingham, was asked whether she was ''concerned about this rhetoric'' from Mr Trump.
She said: ''We've consistently said that the programme that North Korea has in relation to nuclear weapons and ballistic missiles is reckless.
''This is illegal and we are working with the international community, including with the United States, to bring as much political and economic pressure to bear on North Korea to see them change course.''
Earlier on Tuesday, Mr Trump sounded open to the possibility of an inter-Korean dialogue after Mr Kim made a rare overture towards South Korea in his new year address.
But Mr Trump's ambassador to the United Nations insisted talks would not be meaningful unless the North was getting rid of its nuclear weapons.
Liberal Democrat MP Layla Moran said: "After a year in office it has become quite clear that Donald Trump is making the world less safe.
"His ham-fisted bully-boy diplomacy is leaving a trail of destruction in his wake. People struggling through a lifetime of conflict deserve better than a petulant child running a world superpower.
"The world would be a better place if only he could just show some restraint. Instead we will spend years having to pick up the pieces."
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