Palestinian medical officials and the militant group Hamas say four Palestinians have been killed in an explosion near a beach outside Gaza City.
Officials say the casualties included at least two Hamas militants and a girl. At least 15 other people were wounded.
Friday's attack occurred near a car being used by Hamas members, but the cause of the explosion was not immediately known.
It was the third blast of the day in Gaza, after a relatively calm period that followed a cease-fire between Israel and Hamas.
Earlier, an explosion outside a cafe killed a passerby and wounded at least three others. Another explosion took place a few minutes later outside the home of a Hamas politician, Marwan Abu Ras. No one was injured.
Palestinian officials say gunmen carried out both of those blasts.
Hamas took control of the Gaza Strip last year.
The area has been mostly calm since an Egyptian-brokered truce between Israel and Hamas went into effect last month. However, Islamic extremists in Gaza have been waging a campaign against cafes and shops that sell or play music deemed unsuitable, as well as against Christian institutions.
Some information for this report was provided by AFP, AP and Reuters.