WASHINGTON (AFP) - International Monetary Fund (IMF) chief Christine Lagarde said Thursday that the possibility that Britain would vote to pull out from the European Union poses risks for the already weak world economy.

"The risk of Brexit is a worry because it's uncertainty," Lagarde told a New York audience.

"The outcome of any new regime is totally unknown... It's a worry," she said.

Britain will vote on June 23 in a referendum on support for splitting with the European Union, due to what many British believe are unfair burdens and limited benefits that come with membership.

But the vote has raised worries that it could create new barriers to economic growth at a time when the world economy shows more signs of weakening.

"It's one of the risks that we have on the horizon," said Lagarde, who earlier this week warned that global growth is "too fragile" and called on advanced economies to expand fiscal stimulus efforts.

Lagarde added on Thursday that she was "not encouraged" by a Dutch referendum on Thursday in which voters opposed an EU pact with Ukraine, a result seen as favouring anti-EU forces.