(see related) Terni, June 5 - Vice Premier and Interior Minister Angelino Alfano ordered an investigation Wednesday after the mayor of the Umbrian city of Terni was struck on the head during a clash between police and protesting steelworkers. Leopoldo Di Girolamo required two stitches to close the cut on his head sustained earlier in the day. Alfano's office said he called the mayor to check on his health and express regret for what happened. Alfano also said he wanted to get to the bottom of what happened. It was not immediately clear who struck the mayor as police closed in on steelworkers who were marching towards the city's main rail station.