Defeated Republican presidential candidate Mitt Romney has urged his supporters to avoid "partisan bickering and political posturing".
In his concession speech given to a subdued ball room in Boston, Massachusetts, Romney said: "Thank you my friends, thank you so very much. I have just called President Obama to congratulate him on his victory. His supporters and his campaign also deserve congratulations.
"I wish all of them well, but particularly the president, the first lady and their daughters.
"This is a time of great challenges for America, and I pray that the president will be successful in guiding our nation."
Ryan also thanked his vice presidential running mate, congressman Paul Ryan, saying he hoped he would continue to use "his intellect and his hard work and his commitment to principle" for the good of the nation.
"The nation, as you know, is at a critical point. At a time like this we can't risk partisan bickering and political posturing," he said.
"Our leaders have to reach across the aisle to do the people's work and we citizens also have to rise to the occasion."
Governor Romney said: "I believe in America. I believe in the people of America, and I ran for office because I am concerned about America.
"This election is over, but our principles endure. I believe that the principles upon which this nation are the only sure guide to a resurgent economy and to a new greatness."
Romney added: "Thank you and God bless America. You guys are the best, thank you so much. Thanks guys."