Hillary Clinton EU referendum
Democratic frontrunner Hillary Clinton becomes latest political heavyweight to show her support for Britain to stay in the EU Mary Schwalm/Reuters

US presidential candidate Hillary Clinton has echoed President Barack Obama's views throwing her weight behind the campaign for Britain to stay in the EU. Urging against a Brexit vote, the Democratic frontrunner said she "values a strong British voice" in Europe.

She is the latest political heavyweight to wade into the EU referendum prompting a welcome message from No 10.

Clinton's policy adviser Jake Sullivan said in a statement to the Observer: "Hillary Clinton believes that transatlantic co-operation is essential and that cooperation is strongest when Europe is united. She has always valued a strong United Kingdom in a strong EU. And she values a strong British voice in the EU."

The former US secretary of state's stance was revealed a day after Obama had strongly appealed to the UK citing economic and security issues. Clinton, who is most likely tipped to be the Democratic contender, has made foreign policy a cornerstone of her presidential campaign.

Clinton's views come at a time when there is increasing backlash against Obama's three-day trip, which angered the Leave supporters. The American president incurred their wrath after he said the UK would be at the "back of the queue" when it comes to US trade if Britain chooses Brexit in the June referendum. His remarks were criticised by those who have been lobbying for Brexit calling him "hypocritical" and a "lame duck president".

Subsequent to Clinton's support, a Downing Street source told the Guardian: "Not only do you have the serving US president setting out why the UK is better off staying in the EU, but now those who aspire to be president too. Hillary Clinton worked with the UK as secretary of state for a number of years and saw firsthand how the UK's influence was magnified by the role we played in the EU."

Earlier, Clinton's husband and former US president Bill Clinton said he is opposed to the idea of Britain leaving the EU.