WASHINGTON — Daimler AG said Monday that the head of Mercedes-Benz USA has been fired effective immediately.

The company didn't offer an explanation for his departure, but said he had "been excused from his duties as CEO."

Han Tjan, a Daimler spokesman in New York, said Ernst Lieb "has been relieved of his duties as CEO of Mercedes-Benz USA effective immediately. Daily business operations of MBUSA will be conducted by Herbert Werner — CFO and Vice President Finance, Controlling & IT — until further notice."

Tjan said the company would have no further comment on why Lieb was being removed, reported The Detroit News.

Lieb, 56, has headed the U.S. unit of the German automaker since September 2006.

Lieb was previously president and CEO of then-DaimlerChrysler Australia/Pacific and president and CEO of Mercedes-Benz Canada in 1995.

This month, Mercedes-Benz USA, based in Montvale, N.J., reported its highest ever September sales, selling 23,897 vehicles — a 15.6 percent jump over a year ago.

In the first nine months of 2011, Mercedes-Benz has sold 183,711 vehicles — an 11.1 percent increase over the same period last year.

In August, Lieb told reporters he predicted Mercedes-Benz would be the U.S.'s best-selling luxury brand, outselling BMW in 2011. Mercedes-Benz has held about a 5,000-vehicle lead over its German rival.

Lieb said in February the company is spending $1.4 billion to help 300 of its 353 dealerships renovate their facilities. It also brought all its dealers to Germany in April to show them the company's future product plans.

Earlier this month, Lieb was in New Orleans to announce the company's 10-year deal for naming rights for the Superdome, where the New Orleans Saints play. The deal, according to the Times-Picayune, is reportedly worth between $50 million and $60 million.