ANKARA (Reuters) - Seven people were wounded when an explosion hit a shuttle bus carrying prison guards in the Turkish coastal province of Izmir on Thursday, and authorities were investigating a possible terrorist attack, the local mayor said. The bus was hit as it passed a garbage container at around 7:40 a.m. (0440 GMT), Levent Piristina, the mayor of Izmir s Buca district, said on Twitter. Photographs he posted on social media showed its windows blown out and its windscreen shattered. The force of the blast appeared to have blown out some of the bus s panels, and the nearby street was littered with debris.  We are getting information from police sources and they are focusing on the possibility of a terrorist attack,  he said, adding that all seven wounded were in good condition. Both state-run TRT Haber and private broadcaster Dogan news agency said the explosion was caused by a bomb placed in the garbage container that exploded when the shuttle bus passed. No one immediately claimed responsibility. Both Kurdish militants and jihadist Islamic State militants have carried out suicide and bomb attacks in major Turkish cities in recent years. Kurdish militants have previously targeted buses carrying security personnel.  In December, a bomb killed at least 13 soldiers and wounded more than 50 when it ripped through a bus carrying off-duty military personnel in the central city of Kayseri, an attack the government blamed on Kurdish militants. The Kurdistan Workers Party (PKK), considered a terrorist organization by the United States, Turkey and the European Union, has waged a three-decade insurgency against the Turkish state. The outlawed PKK wants autonomy for Turkey s largely Kurdish southeast. 