Mr Obama could benefit from Biden's foreign policy clout, analysts

Mr Obama's choice, confirmed on his website and with a text message to supporters, comes ahead of next week's Democratic Party convention.

Mr Biden, a 65-year-old veteran lawmaker, is highly respected on foreign policy issues.

Republican contender John McCain could announce his choice next week.

Speculation is mounting that Senator McCain may name his running mate on 29 August, his 72nd birthday and a day after the Democrats wrap up their convention in Denver, Colorado.

Mr Obama and Mr Biden are due to appear together as running mates for the first time at a rally which has got under way in Springfield, Illinois.

'Impressive record'

The announcement came shortly after several US media networks began reporting that Mr Biden had been chosen.

"Barack has chosen Joe Biden to be his running mate," a brief statement on Mr Obama's campaign website said.

"Joe Biden brings extensive foreign policy experience, an impressive record of collaborating across party lines, and a direct approach to getting the job done," it said.

Mr Biden has represented the state of Delaware in the US Senate since 1972.

JUSTIN WEBB'S AMERICA Joe Biden is Vladimir Putin's contribution to American politics

He is known as a strong orator and chairs the Foreign Relations Committee - something analysts say would balance Mr Obama's self-confessed lack of foreign policy experience.

The son of a car salesman, he is also expected to appeal to the blue collar workers with whom Mr Obama has struggled to connect.

The senator ran against Mr Obama and Senator Hillary Clinton for the presidential nomination but dropped out after failing to gain enough support.

OFFICE OF THE VICE-PRESIDENT Second-highest executive officer in the United States Assumes the top role if the president cannot continue in office One of four statutory members of the National Security Council

Hillary Clinton, who had been touted as a possible running mate, said Senator Biden would be a "purposeful and dynamic vice-president".

"In naming my colleague and friend Senator Joe Biden to be the vice presidential nominee, Senator Obama has continued in the best traditions for the vice-presidency by selecting an exceptionally strong, experienced leader and devoted public servant," she said in a statement.

The McCain camp called the choice of Mr Biden an admission by Barack Obama that he was not ready to be president.

"Biden has denounced Barack Obama's poor foreign policy judgement and has strongly argued in his own words what Americans are quickly realising - that Barack Obama is not ready to be president," McCain campaign spokesman Ben Porritt said in a statement.

John McCain has reportedly not yet settled on a running mate.

Minnesota Governor Tim Pawlenty and former Massachusetts governor Mitt Romney are reported to be under serious consideration for the role.