(Reuters) - U.S. Midwest manufacturing activity unexpectedly strengthened to its strongest level in a little over three years in June, an index jointly developed by MNI Indicators and ISM-Chicago released on Friday showed.

The Chicago Purchasing Management Index, also known as the Chicago Business Barometer, climbed to 65.7, its highest since May 2014, from 59.4 in May. Analysts polled by Reuters had forecast a figure of 58.0 for June.