Assume that referendum is going to stick: Barack Obama on Brexit

US President Barack Obama said on Saturday he believed that Britain would quit the European Union after the Brexit referendum despite speculation the vote could somehow be reversed.

"I think we have to assume that a referendum having been passed with a lot of attention, a lengthy campaign and relatively high participation rates is going to stick," Obama said when asked if Britain could go back on the vote.

The Brexit vote shocked Britain's allies, with Obama having strongly backed the remain camp ahead of last month's referendum, citing the possible impact on Britain's key role in world affairs as a major concern. "We will remain close friends, allies, partners, continue to have strong relationships on both sides of the channel," Obama said at the close of a NATO summit in Warsaw, the last of his presidency.

"Our primary interest is to make sure that the negotiations and this process are as orderly and as sensible as possible."

On Friday, Obama insisted that Brexit would not undermine Britain's role in NATO but urged London and Brussels to avoid "protracted, adversarial negotiations" over their divorce. "How the negotiations work, I think is going to be up to the parties involved," the president said Saturday.