Boris Johnson has prompted outrage after he said a Libyan city could be transformed into the new Dubai once "they clear the dead bodies" away.

The Foreign Secretary’s off-colour comment drew gasps and shocked laughter from the audience at a global trade fringe event at the Conservative conference.

Theresa May was urged to sack him for his latest gaffe, which critics said proved that Mr Johnson - arguably the UK's top diplomat - was not fit to represent Britain on the world stage.

The remarks are the latest in a string of diplomatic blunders by Mr Johnson, coming days after he was ticked off by the British Ambassador to Burma for reciting a colonial poem in the one of the country's most sacred temples.

Asked about a recent trip to the North African country, Mr Johnson said: "It's got real potential and brilliant young people who want to do all sorts of tech.

"There's a group of UK business people actually, I don't know whether you will have come across this, wonderful guys, who want to invest in Sirte on the coast, near where Gaddafi was actually captured and executed, as some of you may have seen.

“They have a got brilliant vision to turn Sirte, with the help of the municipality of Sirte, into the next Dubai.

“The only thing they’ve got to do is clear the dead bodies.”

Mr Johnson then tried to claim there was “an optimism" in the Libyan city, a former Islamic State stronghold, before host Baroness Stroud, a former special adviser to ex-Cabinet minister Iain Duncan Smith, said: "Next question."

The Legatum Institute chief executive officer added: "The dead bodies was the move on moment."

Shadow Foreign Secretary Emily Thornberry condemned the comments as "unbelievably crass, callous and cruel" after thousands of civilians and hundreds of government soldiers were killed when Sirte was captured from the Islamic State less than a year ago.

She said: "For Boris Johnson to treat those deaths as a joke - a mere inconvenience before UK business people can turn the city into a beach resort - is unbelievably crass, callous and cruel.

"If these words came from the business people themselves, it would be considered offensive enough, but for them to come from the Foreign Secretary is simply a disgrace.

"There comes a time when buffoonery needs to stop, because if Boris Johnson thinks the bodies of those brave government soldiers and innocent civilians killed in Sirte are a suitable subject for throwaway humour, he does not belong in the office of Foreign Secretary."

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Her concern was echoed by Liberal Democrat deputy leader Jo Swinson, who added: "Diplomacy is a basic requirement for the role of Foreign Secretary.

"This latest unbelievably crass and insensitive comment about an issue of such importance is further proof Boris is not up to the job.

"Theresa May needs to get her house in order and sack him."