LONDON (Reuters) - U.S. President Barack Obama said he was confident that Britain and the European Union would be able to agree an orderly transition to a new relationship after last month's Brexit vote.

"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," Obama said in an article for the Financial Times, calling upon NATO to stand united against global challenges.

"The special relationship between the US and the UK will endure. I have no doubt that the UK will remain one of Nato’s most capable members."

Obama urged NATO to unite following Britain's June 23 vote to leave the EU and stressed that the alliance between the United States and its closest ally in Europe would endure Brexit.

(Reporting by Alistair Smout; editing by Guy Faulconbridge)