United Kingdom's Prime Minister Cameron addresses a news conference after the EU Summit in Brussels, Belgium, June 28, 2016. [Photo/Agencies]

BRUSSELS - Expressing regret and sadness over Britain's decision to leave the European Union, Prime Minister David Cameron said on Tuesday the country would not turn its back on Europe and would instead build the strongest ties it could.

At what he said would be his last EU summit, Cameron told a news conference that as a democrat he had accepted the will of the people and other leaders had also respected the choice in a mood "of sadness and regret".

"I threw myself in head, heart and soul to keep Britain in the European Union and I didn't succeed," he said. "And when you lose you have to say right I've lost that argument, I've lost that ... debate and it's right to hand over to someone else who will take the country forward.

"Now of course I am sad about that, but frankly I'm more concerned about Britain getting its relationship right with Europe."

Britain will seek a close relationship with EU in the future, he said.

He stressed Britain would leave the European Union, seeking to quash suggestions it could avoid a Brexit or preserve access to the bloc's prized single market if it curbed flows of migrant workers from the EU.

"If you want the full benefits of the single market, you'll have to be part of every part of it," he said.