The widely expected announcement came in the form of a video released by the Clinton campaign today.

"I'm with her, I'm fired up and I cannot wait to get out there and campaign with Hillary," the President says.

The endorsement came within hours of Mr Obama holding talks at the White House with Mrs Clinton's Democratic rival Bernie Sanders.

The Vermont Senator vowed to continue his fight for the Democratic nomination afterward, but also said he looked forward to working with Mrs Clinton during the general election.

Mr Obama had been expected to urge Mr Sanders to call time on his campaign in a bid to fully shift the focus of the 2016 election on the upcoming showdown between Mrs Clinton and presumptive Republican nominee Donald Trump.

In his Clinton endorsement, which appeared to be recorded in advance of the President's meeting with Mr Sanders, Mr Obama praised the senator for running an "incredible campaign".

He said that he personally thanked Mr Sanders for shining a spotlight on issues like economic inequality, the outsized influence of money on our politics and for bringing young people in to the process.

"Embracing that message is going to help us win in November," Mr Obama said.

The President made no mention of Mr Trump in his endorsement, but aides have said he is eager to leave the sidelines and join the fray against brash billionaire.

Mr Trump noted Mr Obama's endorsement of "Crooked Hillary" on Twitter, saying the President may want "four more years of Obama - but nobody else does!"

In perhaps a sign of what can be expected in the months leading up to the November election, Mrs Clinton countered with a tweet of her own, urging Mr Trump to delete his account.