US presidential candidate Bernie Sanders has admitted that he faces an "uphill fight" to win the Democratic nomination. Sanders was speaking at a rally in Vallejo in California on 18 May.

The Vermont senator said, "As of today we have won over nine million votes, and almost 46 percent of all of the pledged delegates – the real delegates – that were voted on by the people. Now, I don't deny that for a moment that we have an uphill fight in order to win a majority of the pledged delegates, but we are going to fight in California and the remaining five other states to get every vote and every delegate we can".

The final round of major primaries take place on 7 June, including key swing state California. Both Sanders and Clinton picked up wins on 17 May, in Oregon and Kentucky respectively.

Clinton currently leads Sanders in the number of delegates, with 2,293 to his 1,533 as of 19 May. However, the race is much closer than expected, as it was thought that Clinton would secure the nomination much earlier.

Sanders has prevented her from doing so by doing much better than predicted – no one expected him to make the inroads that he has for so long. In the race for Democratic nomination, candidates require 2383 delegates to win.

Controversial New York business mogul Donald Trump has all but secured his nomination as the Republican Party candidate. Trump will now face either Clinton or Sanders in the race for the White House in November.