BOSTON, Massachusetts: Republican challenger Mitt Romney conceded defeat in the US election early on Wednesday, telling supporters that he had called President Barack Obama to congratulate him on his victory.

"His supporters and his campaign also deserve congratulations," Romney said in a brief address at his election watch party in Boston.

"I wish all of them well but particularly the president, the first lady and their daughters."

It was a quick, underwhelming end to an 18-month campaign that began on a farm in New Hampshire, survived brutal Republican infighting during the party primaries early this year and a barrage of negative attack ads by the Obama camp, and rose to give the incumbent a serious scare weeks before the election.

Romney was neck-and-neck with the president for a considerable part of the campaign, but despite repeated trips to swing states like Colorado, Ohio, Florida, and Virginia, Obama held on to leads in the battlegrounds, which eventually became the challenger's undoing.

As of 0700 GMT Wednesday, Obama won 303 electoral votes, compared to 203 for Romney, with only key battleground of Florida outstanding. Two hundred seventy are needed to with the White House.

"This election is over, but our principles endure," said Romney, a former governor of Massachusetts who said that he believed smaller government, limited regulations and lower taxes could create more jobs and bring a speedier economic recovery.

"I so wish that I had been able to fulfill your hopes to lead the country in a different direction, but the nation chose another leader, and so Ann and I join with you to earnestly pray for him and this great nation," Romney said to cheers and applause.

Several members of Romney's senior staff stood next to the stage, many stone-faced and somber, as the Republican nominee addressed his supporters.

Romney returned to a theme that he began injecting into his stump speeches in the closing two weeks of the campaign: the need for greater bipartisanship in Washington.

"At a time like this, we can't risk partisan bickering and posturing," he said.

"Our leaders have to reach across the aisle to do the people's work and we citizens have to rise to the occasion."

Romney also thanked his running mate, Rep. Paul Ryan of Wisconsin, as well as wife Ann Romney, his tireless surrogate on the campaign trail whom he called "the love of my life."

"She would have been a wonderful first lady," he mused, to loud applause.

Romney's comments were brief and basic, and it was not immediately clear if he had written a concession speech.

Earlier in the day, when asked by reporters on his campaign plane whether he had two speeches ready to go for Tuesday night, he said that he was confident of defeating Obama and had penned an 1,118-word victory speech.

After stepping back from the podium, Romney turned around and kissed his wife, gave Ryan a handshake and a hug, and then stepped into the embrace of his family.