Former US president Barack Obama endorsed his fellow Democrat Kamala Harris' bid for the White House on Friday, delivering a major boost to her campaign to beat Donald Trump in November's presidential election, reports BSS.

"Earlier this week, Michelle and I called our friend Kamala Harris. We told her we think she'll make a fantastic President of the United States, and that she has our full support," Obama said on social media platform X.

The influential former leader was one of the last Democratic heavy hitters to offer his endorsement, with Harris having already received the backing of President Joe Biden on Sunday to take his place on the ballot.

Obama's backing will add to the growing momentum behind Harris' campaign, which has enjoyed a groundswell of support since she announced her 11th-hour candidacy.

Harris, 59, jumped into the election after weeks of turmoil over 81-year-old Biden, who bowed out after a dismal debate performance against Trump accelerated concerns over his mental capacity and persistently low polling numbers.

The country's first woman vice president -- who is seeking to make history again in November -- launched a blistering attack on Trump and his "extremist" Republicans as she addressed teachers Thursday.

The momentum appeared to catch Trump off guard, with the bombastic Republican refusing to schedule a debate with Harris, saying Thursday night it would be "inappropriate" until she was officially named the Democratic nominee.

"Democrats very well could still change their minds," Trump campaign spokesman Steven Cheung said in a statement.

Harris, a former top prosecutor for California, chided her opponent on X, saying: "What happened to 'any time, any place?'"

She had previously said of a potential September 10 face-off: "I'm ready. So let's go."

Bd-pratidin English/Tanvir Raihan