The Israeli incursion and air attacks drew rocket fire from the Hamas-controlled enclave, with sirens sounding in Israeli communities along the border. The military said its defenses intercepted two launches. There were no immediate reports of injuries or damage on the Israeli side of the frontier.

The violence prompted Israeli Prime Minister Benjamin Netanyahu to cut short a visit to Paris, where he had been gathering with world leaders for a World War One commemoration.

Hamas said the incident began when assailants in a passing car opened fire on a group of its armed men, killing one of its commanders. Hamas gunmen gave chase as the car sped back towards the border with Israel, Hamas said in a statement.

During the pursuit, Israeli aircraft fired more than 40 missiles in the area, according to witnesses.

Medics and Hamas officials said at least six people were killed including commander Nour Baraka and another member of the group. It was unclear if the other fatalities included gunmen.

The Israeli military said in a brief statement that: "During IDF (Israel Defense Forces) operational activity in the Gaza Strip, an exchange of fire evolved."

A return by Israel to a policy of targeting individual Hamas commanders - tactics largely abandoned in recent years - could significantly raise tensions along the border.

Violence has flared frequently on the frontier since Palestinians began weekly protests on March 30. Egypt, Qatar and the United Nations have been trying to broker a long-term ceasefire.