FILE PHOTO: US Democratic presidential nominee Senator Barack Obama (D-IL) and Senator Hillary Clinton (D-NY) wave at a campaign rally in Orlando, Florida, October 20, 2008. [Photo/Agencies]

WASHINGTON - US President Barack Obama endorsed fellow Democrat Hillary Clinton for president on Thursday, saying he did not think there had ever been a nominee so qualified for the White House.

"I'm with her. I am fired up, and I cannot wait to get out there and campaign for Hillary," Obama said in a video released by the Clinton campaign.

The endorsement increases pressure on Clinton's rival in the Democratic primary contest, US Senator Bernie Sanders, to concede the race so the party can focus on campaigning against Donald Trump, the Republican Party's presumptive nominee for the Nov 8 election.

Obama had been expected to support Clinton since she won enough delegates this week to clinch the Democratic nomination and become the first woman to lead a major US party as its presidential nominee.

The president remains popular with voters, and his endorsement will come as a significant boost to Clinton. Obama and Clinton were rivals during the 2008 Democratic primary that Obama won. Clinton went on to serve as Obama's secretary of state during his first term in office.

Sanders, who met with Obama at the White House earlier on Thursday, said afterward he would work with Clinton to defeat Trump. Sanders said, however, that he would stay in the race to compete in the final Democratic primary vote in Washington, D.C., on June 14.