(CNN) — A missile test involving Britain’s Trident nuclear deterrent system ended in failure off the coast of Florida last year, a US defense official with direct knowledge of the incident told CNN on Monday.

The official told CNN that the incident, which happened in an the area off the Florida coast used by the US and the UK for missile tests, did not include a nuclear warhead as it was a test.

Britain’s Sunday Times newspaper reported that the missile veered towards the US coast but the US official told CNN the trajectory was part of an automatic self-destruct sequence.

The official said the missile was diverted into the ocean to self-destruct — an automatic procedure when missile electronics detect an anomaly.

British Prime Minister Theresa May has come under fire for refusing to answer questions about the failed test.

On Sunday, May was asked four times during an interview with the BBC’s Andrew Marr Show whether she knew the missile had gone off course before a vote on renewing the deterrent in parliament.

She refused to answer the question, which prompted heavy criticism from those opposed to Trident.

Scotland’s First Minister Nicola Sturgeon, tweeted: “This is a hugely serious issue. There should be full disclosure of what happened, who knew what/when, and why House of Commons wasn’t told.”

On Monday, a spokeswoman for May said she was briefed on a test of Trident when she came into office.

The Prime Minister and the Defence Secretary are routinely informed about tests and their outcome, May’s spokeswoman told reporters on Monday.

“These are known as a ‘demonstration and shakedown’ test. This test was in June (2016) under the last prime minister (David Cameron). On taking office the current Prime Minister (Theresa May) was briefed on a range of nuclear issues, including this. This test saw the submarine and crew successfully tested and certified.”

The decision to spend £40 billion to renew Trident was taken in a parliamentary vote last July and passed 472 votes to 117.

May will become the first world leader to meet with new US President Donald Trump when they hold talks in Washington on Friday.

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