An explosion at an anti-government march in the Thai capital Friday injured at least 31 protesters participating in a Bangkok “shutdown” campaign, hospital sources said.The device was thrown into the midst of a march in central Bangkok, and exploded about 100 metres behind protest leader Suthep Thaugsuban, who was not wounded, BlueSky TV reported.“There were at least 31 people injured by the explosion,” said an official at the Erawan Emergency Centre. “Most received minor injuries to their legs.”Suthep, a former parliamentarian with the Democrat opposition party who heads the People’s Democratic Reform Committee (PDRC), has been holding street protests in the capital since early November to force the resignation of caretaker Prime Minister Yingluck Shinawatra and her cabinet.