ST. PAUL  (AP) - State Sen. Amy Koch says she's stepping down as Senate majority leader and won't seek reelection next year.

Koch made the surprise announcement Thursday in a letter to fellow Republican senators and GOP staff. The Republican from Buffalo didn't directly give a reason but wrote that the past year was "challenging, exciting and exhausting."

Koch did not immediately respond to a message left on her cell phone.

As the top Senate Republican, Koch was a face of the party during last summer's budget standoff with Democratic Gov. Mark Dayton that led to a government shutdown. She was new to leadership after recruiting a slate of GOP candidates who knocked off Democratic incumbents in 2010 and handed Republicans control of the Senate for the first time in decades.

(Copyright 2011 by The Associated Press. All Rights Reserved)