US President Barack Obama expressed confidence Friday that Britain and the European Union will manage an "orderly transition" after the country's shock decision to leave the bloc.
The June 23 referendum vote for Britain to leave the EU has raised concerns about the stability and future of the bloc.
The vote "raises significant questions about the future of European integration," Obama wrote in the Financial Times newspaper, ahead of talks in the Polish capital Warsaw with top EU officials.
"As difficult as it will be, I am confident that the UK and the EU will be able to agree on an orderly transition to a new relationship, as all our countries stay focused on ensuring financial stability and growing the global economy," he added.
Obama is scheduled to meet EU President Donald Tusk and European Commission President Jean-Claude Juncker in Warsaw on Friday morning, before attending a NATO summit. Obama is expected to hold talks with British Prime Minister David Cameron there.
"I have no doubt that the UK will remain one of NATO's most capable members — a nation that pays its full share for our common security and is a leading contributor to alliance missions," Obama wrote.
"Given the current threats facing Europe, I fully expect that Britain will continue to be a major contributor to European security," he added. "The special relationship between the US and the UK will endure."
The meeting with Tusk and Juncker will be "a very timely opportunity to discuss the aftermath of the Brexit vote and our continued, very strong support for the European project," US Deputy National Security Advisor Ben Rhodes said.
The talks will focus on how to "ensure the health and vitality of the European project moving forward, and what steps Europeans will be taking to try to ensure that the EU remains in the best shape possible," said Charles Kupchan, Obama's advisor on European affairs.
The leaders will also review negotiations on the mammoth and controversial free trade agreement being negotiated between the US and EU, commonly known as TTIP.
Tusk and Juncker intend to seek "movement from the US on issues important to us," a senior EU official said on condition of anonymity. But there has been growing scepticism about whether a deal is possible before the US presidential election in November.
Other issues to be discussed include terrorism, migration, economic issues and Russia, the White House said.
"Europe will remain a cornerstone of America's engagement with the world," Obama wrote. "The US and the EU have the largest trade and investment relationship in the world and our co-operation will be essential to stimulating global growth and reducing inequality."
The trip is Obama's last planned visit to Europe before he leaves office in January.