A Palestinian leader of an Islamic extremist group inspired by Al Qaeda was killed in an apparent Israeli airstrike in Gaza City on Wednesday, according to the Israeli military.

The car in which the militant was traveling exploded near a central police compound. Hamas officials said an Israeli missile fired from a drone caused the blast. The Israeli military gave no details about how the attack, which ended a period of relative calm, was carried out.

The sound of the blast echoed through the city, and a column of black smoke and fire rose from the car, which was destroyed.

The militant was identified as Mohammed al-Nemnem, 27, a senior member of the Army of Islam, an extremist group.

Barak Raz, a spokesman for the Israeli military, described Mr. Nemnem as “a ticking bomb” and said that Israel mounted the attack against him on Wednesday because it “had the intelligence and means to carry out the operation.”

The Israeli military said in a statement that Mr. Nemnem had been “personally involved in directing several terrorist attacks against Israeli targets in recent years.” More recently, the military said, he was involved in “directing a terror attack against American and Israeli targets in the Sinai Peninsula, in cooperation with Hamas elements in the Gaza Strip.”

It gave no further details about the timing or location of that attack, or whether it had indeed been carried out.

Hamas, the Islamic militant group that rules Gaza, won Palestinian parliamentary elections there in 2006, and then took full control in 2007. Its relations with some of the smaller and more extreme splinter groups have become tense, at times leading to open confrontation.

Also on Wednesday, a Hamas police officer shot dead a Palestinian salesman and critically wounded his assistant in a market in the Beach refugee camp, west of Gaza City.

A spokesman for the Hamas police said the police officer had intervened to stop a quarrel when a bullet was accidentally discharged from his gun. But witnesses said that the police officer had been involved in a “furious” argument with the salesman, Alaa al-Sourri, before shooting at him.