Donald Trump made an unexpected appearance Tuesday on a White House rooftop and joked about installing nuclear missiles at a time of escalating tensions with Russia.

The US president, flanked by bodyguards and under the protection of snipers, strolled for 20 minutes on the flat roof above the press room as he looked across to the site of his proposed new ballroom.

Asked why he was on the roof, he replied he was just "taking a little walk."

Quizzed about what he intended to build, he joked "nuclear missiles," before appearing to mimic the launch of a weapon with his arm.

The United States and Russia have engaged in heated rhetoric for several days.

Trump last week ordered the deployment of two nuclear submarines near Russia in response to remarks he deemed provocative by former Russian

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