PARIS (REUTERS) - French President Francois Hollande on Wednesday (Nov 9) congratulated Donald Trump on his shock victory in the US presidential election, but warned the result would open up a period of uncertainty.

"I congratulate him as is natural between two democratic heads of state," said Hollande. "This American election opens a period of uncertainty."

France would be vigilant and frank in its talks with the new administration on international issues, he said, adding that Trump's victory showed that France needed to be stronger and that Europe needed to be united.

A presidential official said Hollande had spoken to German Chancellor Angela Merkel before making his declaration.