Warning that the last thing the EU needed was another crisis, Steinmeier said on Wednesday that a British vote to leave would "shake the Union," adding that a concerted effort would be required to ensure the bloc's stability.

At a news conference with his French counterpart, he and Jean-Marc Ayrault voiced hope that British voters would decide to remain in the EU in the June 23 referendum. "That would be the right decision to make," Steinmeier said.

His comments were backed up by German Defense Minister Ursula von der Leyen, who told the weekly "Die Zeit" that "if Britons were to leave the EU, this heads-in-the-clouds mentality would dominate."

She said Britain's "skepticism," its "understatement" and its "grandiose pragmatism" were ideal substitutes for Germany's "excessive enthusiasm" on European matters.

The two ministers' comments echoed other senior German politicians, who have become more vocal in recent weeks as opinion polls suggest the UK mood might be shifting towards an EU exit.

Merkel's call to voters

Last week, German Chancellor Angela Merkel said she hoped that British voters would decide to remain in the bloc.

"From my point of view, Britain remaining in the European Union is the best and most desirable thing for us all," Merkel said.

But German pleas were matched with a warning that Britain couldn't count on remaining a member of the single market in the event of a 'Leave' vote next Thursday.

Many Brexit campaigners have suggested that Britain would still seek to be a member of the European Economic Area, but German Finance Minister Wolfgang Schäuble warned over the weekend that the UK would not be given that option if it quit.

Germany has also voiced concerns that a Brexit could cause a domino effect, leading to other countries leaving or seeking similar public votes on the issue.

mm/msh (AFP, Reuters)