Gordon Brown today called on America to seize a "new dawn in collaborative action" to create a stronger relationship with Europe.

In a keynote speech on the final day of his official visit to the US, the Prime Minister urged America to put itself at the head of the movement to reshape the world's big institutions to meet the new global challenges of the 21st century.

Speaking to an audience of 350 invited guests at the John F Kennedy Presidential Library in Boston, he urged them to work together to overhaul the post-Second World War structures of the United Nations, the International Monetary Fund and the World Bank.

During his visit, Mr Brown met the main contenders to succeed President George Bush - John McCain, Barack Obama and Hillary Clinton - and his speech was pitched as a direct appeal to them.

"American leadership is and will be indispensable," he said.

"And now is an opportunity for an historic effort in co-operation; a new dawn in collaborative action between America and Europe - a new commitment from Europe that I believe all European leaders can work with America to forge stronger transatlantic links.

His comments reflect a belief that the current generation of leaders in France, Germany, and Italy are now prepared to move forward on institutional reform.

"Today, as we face these new global challenges, the tantalising possibilities of a world where as John F Kennedy put it, the strong are just, the weak secure and the peace preserved are matched only by the terrifying risks of us failing to seize this moment," he said.

"For the first time in human history we have the opportunity to come together around a global covenant to reframe the international architecture and build the truly global society."