BERLIN (AP) -- Germany's most populous state is toughening a ban on smoking in bars and restaurants, closing loopholes in its five-year-old restrictions.

North Rhine-Westphalia, a western region of about 18 million people that includes Cologne, Bonn, Duesseldorf and the Ruhr industrial area, introduced its smoking ban in 2008 -- around the same time other German states put similar restrictions into effect.

The state legislature on Thursday approved a toughened version to take effect next May. It shuts loopholes that allowed customers to light up in establishments that designated themselves smoking bars, in special rooms set aside for smokers or in beer tents, among other things. The center-left state government said the original ban had so many loopholes it didn't effectively protect nonsmokers.

In future, exceptions will be allowed only for private parties.

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