WASHINGTON (AFP) - US President Barack Obama on Friday congratulated David Cameron on an "impressive electoral victory," after the British prime minister secured a new term in power.

"The special and essential relationship between the United States and the United Kingdom is rooted in deep and abiding shared interests and values," Obama said in a statement.

"I have enjoyed working closely with Prime Minister Cameron on a range of shared interests these last several years, and I look forward to continuing to strengthen the bonds between our countries."

Cameron's Conservative party won victory, despite widespread predictions of a tie with the Labour party.

Cameron has promised to hold a referendum on Britain's European Union membership in 2017, a vote that could have profound repercussions for the country's role on the world stage.

The White House had earlier said that Obama was "proud" of the relationship he has forged with Cameron and looked forward to continued close ties following the Conservative party's win.

"This is a testament to the strength of a vibrant democracy," White House spokesman Josh Earnest told CNN.

"The President is proud of the strong working relationship that he's developed with David Cameron over the years, and he's looking forward to continuing to strengthen that personal relationship," Earnest said.

He added that the administration also hopes to "continue to deepen the relationship between the American people and the British people because the close relationship of our governments has served the citizens of our country very well."