US Vice President Joe Biden walks back to the Oval Office after Biden announced he will not seek the 2016 Democratic presidential nomination, during an appearance in the Rose Garden of the White House in Washington October 21, 2015. [Photo/Agencies]

WASHINGTON - US Vice President Joe Biden said on Wednesday he would not run for president in 2016, ending months of indecision and removing one of Democratic front-runner Hillary Clinton's biggest potential obstacles to the party's nomination.

Biden, 72, appeared in the White House Rose Garden with his wife Jill and President Barack Obama to say the window for mounting a successful campaign had closed.

Biden's announcement ended a highly public "will he or won't he?" political guessing game about his intentions that had shadowed Clinton's campaign and frozen the support of some Democratic activists and donors.

"While I will not be a candidate, I will not be silent," Biden said. "I intend to speak out clearly and forcefully to influence as much as I can where we stand as a party and where we need to go as a nation."

Biden had been wrestling with doubts about whether he and his family were ready for a grueling campaign while still mourning his son Beau, who died of brain cancer in May. His son had urged him to run.

Making good on his promise to speak out, Biden took a veiled jab at Clinton, chiding Democrats who referred to Republicans as their enemies and saying Democrats would be making a "tragic mistake" if they walked away from Obama's record.

Clinton had listed Republicans among her enemies during last week's presidential debate and had broken with Obama by moving to the left on such issues as the Keystone XL pipeline and the Trans-Pacific Partnership.