LONDON — British and European leaders appealed for calm on Monday as concern over the U.K.’s exit from the European Union and its deepening political crisis triggered further gyrations in financial markets and hit confidence in the economy.

In his first public appearance since Thursday’s referendum, U.K. Treasury chief George Osborne stressed that the country’s economy can withstand the shockwaves created by the vote, and that it is in a far better position than it was at the start of the 2008 financial crisis.

“It will not be plain sailing in the days ahead,” he said. “But let me be clear. You should not underestimate our resolve. We were prepared for the unexpected.”

The leaders of European heavyweights Germany, Italy and France will huddle later Monday to discuss a strategy to handle Britain’s exit, trying to hone a common message that negotiations need to get underway quickly on the exit so as not to continue the uncertainty.