Washington - Republican John McCain quickly conceded defeat in Tuesday's election, congratulating Democrat Barack Obama for his historic victory and urging Americans to help the new president meet the country's challenges.

Speaking from his campaign headquarters in Phoenix, Arizona, McCain told his supporters to cast aside differences with Obama and the Democrats. McCain, 72, said he telephoned Obama, 47, a few minutes earlier to congratulate Obama and his family.

"I wish Godspeed to the man who was my former opponent and will be my next president," McCain said in an address delivered within a few minutes of the closing of polls on the West Coast, when the outcome was obvious.

Obama had captured enough states to easily top the threshold of 270 votes in the Electoral College, becoming the first African- American president after Americans strongly endorsed his message of change.

"We have come to the end of a long journey," McCain told supporters. "The American people have spoken, and they have spoken clearly."

Obama prevailed in the election after capturing Ohio, Florida, Virginia, New Mexico and Iowa, all states won by President George W Bush in 2004. Bush's unpopularity as he prepares to leave office after eight years proved an insurmountable obstacle for fellow Republican McCain.

The Arizona senator thanked his supporters and campaign staff, and praised his vice presidential running mate, Alaska Governor Sarah Palin.

"It is natural, though, to feel some disappointment, but tomorrow we must move beyond it," McCain said. "We fought as hard as we could, and though we fell short, the failure is mine - not yours."

Obama went before supporters in Chicago shortly after McCain spoke, praising the Arizona senator for his resilience on the campaign trail and his dedication to his country as a member of Congress and as prisoner during the Vietnam War.

"Senator McCain fought long and hard in this campaign. And he's fought even longer and harder for the country that he loves," Obama said. "He has endured sacrifices for America that most of us cannot begin to imagine. We are better off for the service rendered by this brave and selfless leader."

McCain acknowledged Obama effectiveness at appealing to average Americans, at raising money and bringing voter turnout to record levels, and for his achievement in becoming the first black to win the presidency.

"I recognize the special significance it has for African- Americans and for the special pride that must be theirs tonight," McCain said, referencing the struggle for civil rights and the days of slavery.

"America today is a world away from the cruel and frightful bigotry of that time," McCain said. "There is no better evidence of this than the election of an African-American to the presidency of the United States."

The outlook for McCain looked grim not long after polls closed in key battleground states tilting toward Obama. The Democrat easily prevailed in Pennsylvania and took Ohio, two states feeling the squeeze of the economic crisis.

Polls had shown that US voters had more faith in McCain on issues of foreign policy and national security, but the financial crisis took centre stage in the final months of the campaign, and Americans clearly believed Obama was better suited to rescue the economy.

McCain expressed his condolences to Obama, whose grandmother who played a major role in his upbringing passed away one day before the election.

"Senator Obama has achieved a great thing for himself and for his country," McCain said. "I applaud him for it, and offer him my sincere sympathy that his beloved grandmother did not live to see this day." (dpa)