Gaza Strip ? A powerful explosion ripped through a car on a busy Gaza City beach Friday night, killing a Hamas field commander and three other people, security officials said.

It was the third unexplained blast of the day in this coastal territory after a relatively calm period since Israel and the Islamic militants of Hamas agreed on a cease-fire last month. A total of five people died from the explosions, and 23 suffered injuries.

No one in Gaza blamed Israel for the violence, indicating it was likely Palestinian infighting.

The late night blast killed Amar Musubah, a Hamas military field commander, and another Hamas militant, Eyad Al-Hia, medical officials said. A child and a fourth unknown individual also died.