Hillary Clinton will abandon her White House bid at the end of the week and throw her support to rival Barack Obama, her campaign said on Wednesday after she said an emotional farewell to her loyal staff.

The announcement came a day after Senator Obama secured enough delegates to clinch the Democratic nomination and as the party coalesced behind the Illinois senator to take the fight to Republican John McCain.

Senator Clinton refused to concede on Tuesday and said she would deliberate in the coming days, but the brief message from her team had an air of finality about her doomed bid to become the first woman president.

"Senator Clinton will be hosting an event in Washington ... to thank her supporters and express her support for Senator Obama and party unity," her campaign said in a statement.

Earlier in the day, US media reported Senator Clinton would abandon her bid for the White House on Friday and concede the race to Senator Obama, but her campaign said Senator Clinton's event would be held on Saturday "to accommodate more of Senator Clinton's supporters who want to attend".

Senator Clinton visited her campaign headquarters in Arlington, in Washington's Virginia suburbs, on Wednesday to inform most of the staff that they would no longer be required after Friday, ABC News said.

Junior staffers were said to be emotional and some were crying at the final confirmation that their 16 months of hard graft had come to naught.

On its website, The New York Times quoted a senior adviser to Senator Clinton as saying the New York senator would most likely suspend her campaign and endorse Senator Obama on Friday at the urging of Democratic members of Congress keen to fight Senator McCain.

Senator Clinton would be bowing to the reality that, after the final primaries were held in Montana and South Dakota, Senator Obama was the Democratic Party's heir apparent for November's election against the Arizona senator.

However, in refusing to concede, she had kept her options open, and Clinton surrogates spent Wednesday talking up her credentials to be Senator Obama's nominee for vice-president.

Senator Clinton sang her rival's praises to a powerful pro-Israel lobby earlier in the day, her clearest admission yet that the race was over.

"Let me be very clear, I know that Senator Obama will be a good friend to Israel," she said, seeking to shed the Illinois senator's perceived weaknesses among Jewish voters.

Senator Obama also heaped praise on his rival for making "history" on the campaign trail, as the two addressed the American Israel Public Affairs Council (AIPAC) within minutes of each other.

Senator Obama told reporters after a visit to the US Senate that he had talked to Senator Clinton in the early hours of the morning.

"We are going to be having a conversation with the coming weeks," he said, adding he was confident the party would be unified by the November election.

On November 4, voters must pick between Senator Obama, 46, a freshman senator and charismatic mixed-race champion of a new political generation, and Senator McCain, 71, a wounded Vietnam war hero asking for one final call to service.

Senator Obama plunged straight into the five-month election battle on Wednesday, crossing swords with Senator McCain over Middle East policy.

Laying out the contours of his presidential program, Senator Obama insisted Jerusalem must remain the undivided capital of Israel, and said he would work to "eliminate" the threat posed by Iran.

"His appearance was very impressive. His words on Jerusalem were very moving," Israeli Prime Minister Ehud Olmert told reporters after meeting President George Bush in the White House.

But less than two hours later, Senator McCain's campaign was on the attack, denouncing Senator Obama for presenting a "rather odd, alternative reality".

"Senator Obama really presents kind of a false choice today, that the only diplomacy that can work is with Iranian leaders," Senator McCain's senior foreign policy adviser Randy Scheunemann told reporters.

Meanwhile, Senator Obama's campaign announced that Caroline Kennedy, daughter of assassinated president John F. Kennedy, had been selected as part of a three-member team searching for a vice-presidential pick.

Obama spokesman Bill Burton said in a statement that the team would also include former deputy attorney-general Eric Holder and James Johnson, a senior Democratic Party insider.

Senator Clinton's campaign chairman, Terry McAuliffe, told MSNBC television that an Obama-Clinton ticket would be "unstoppable". He added: "I think we would have the White House for 16 years."

But former US president Jimmy Carter warned that Senator Obama would make the "worst mistake" if he chose Senator Clinton as running mate.

"That would just accumulate the negative aspects of both candidates," he told The Guardian on its website.

"If you take that 50 per cent who just don't want to vote for Clinton and add it to whatever element there might be who don't think Obama is white enough or old enough or experienced enough or because he's got a middle name that sounds Arab, you could have the worst of both worlds," he said.

AFP