Donald Trump defends Boris Johnson as the UK prime minister comes under growing pressure to resign.

Johnson's opponents on Tuesday lined up to call for his resignation after the UK Supreme Court ruled that he had broken the law by suspending parliament.

Johnson will leave the UN General Assembly in New York early, after the court ruled that the UK parliament is still in session.

Johnson is accused of misleading the queen after he instructed her to shut parliament for five weeks.

Visit Business Insider's homepage for more stories.

Donald Trump has insisted that Boris Johnson will not resign as the United Kingdom's prime minister, following a day in which Johnson found to have broken the law by suspending the Westminster parliament.

Johnson faced growing calls to step down on Tuesday, after the UK Supreme Court ruled that Johnson's decision to shut down Parliament for five weeks was illegal.

The opposition Labour Party leader Jeremy Corbyn was joined by the Scottish and Welsh first ministers in calling for Johnson to step down, amid allegations that he had misled the queen by advising her to suspend parliament.

Johnson will return to the UK early on Wednesday following his address to the UN General Assembly, after the court ruled that Johnson's unlawful action meant that the UK parliament remained in session.

Read more: Boris Johnson told to resign following Supreme Court defeat and become the 'shortest-serving prime minister ever'

However, Trump dismissed the issue as just "another day in the office" for Johnson.

"I know him well," Trump said at a joint press conference between the two men on Tuesday.

"He's not going anywhere. Don't worry about him.

"It's just another day in the office. He's a professional."

After Reuters reporter Jeff Mason asked Trump about the issue, the president accused him of asking a "very nasty question."

Johnson then defended the reporter, "He was asking a question, to be fair, that a lot of British reporters would have asked."

Watch Trump complain about a 'very nasty question' to Boris Johnson