US Vice President Joe Biden says not to run for presidency

US Vice-President Joe Biden will not seek the presidency, he announced in a surprise appearance at the White House on Wednesday.

The news capped months of speculation about whether Biden would challenge Hillary Clinton, his fellow Democrat, former Senate colleague and friend.

"As my family and I have worked through the grieving process," he said referring to the recent death of his son Beau, "I've said all along that it may very well be that that process, by the time we get through it, closes the window on mounting a realistic campaign for president".

"I've concluded it has closed," he was quoted by The Guardian as saying.

Flanked by his wife, Jill, and President Barack Obama, Biden thanked the president for lending him the Rose Garden, and spoke in personal terms about the loss of his eldest son to cancer in May.

"My family has suffered a loss, and I hope there will come a time ... that sooner rather than later, when you think of your loved one, it brings a smile to your lips before it brings a tear to your eyes.

"That's where the Bidens are today."

Biden promised to be active during the campaign.

"I will not be silent. I will speak clearly and forcefully ? on where we stand as a nation."

Biden did not use the speech in the Rose Garden to support the candidacy of Democratic front runner Hillary Clinton, but instead repeated a criticism he has made in recent days of a remark she made at the presidential debate last week that Republicans were the "enemy".

"I believe that we have to end the divisive partisan politics that is ripping this country apart, and I believe that we can," Biden said. "I don't think, as some do, that we should look at Republicans as our enemy. They're the opposition, they're not the enemy."