BEIRUT, Lebanon — A car bomb tore through a parking lot in the heart of Hezbollah territory in the southern suburbs of Beirut on Tuesday morning, a bold attack on Lebanon’s most powerful political and military player. The bombing increased fears that the spillover from the war in neighboring Syria was entering a dangerous new phase.

Some supporters of Hezbollah, the Shiite Muslim militant group and political party, angry at the worst attack in years in a neighborhood it tightly controls, blamed Lebanese or Syrian militants who back the Sunni-led uprising in Syria, which Hezbollah opposes.

The blast, in the Bir al-Abed district, injured 53 people, Lebanese officials said. No one was killed, though the parking lot was near a supermarket where people were shopping for food to break one of the first fasts of the Islamic holy month of Ramadan.

The bombing aggravated fears here that Hezbollah or its supporters would face attacks in response to the group’s military intervention in Syria against the uprising that is challenging its longtime ally President Bashar al-Assad. That conflict has deeply divided Lebanon and strained its fragile political balance, and Hezbollah’s involvement has left some supporters bracing for reprisals and feeling ambivalent about fighting fellow Arab Muslims.