GAZA -- Three sons of Ismail Haniyeh, the head of the Hamas Political Bureau, along with his three grandchildren, were killed in an Israeli airstrike on Gaza City Wednesday.

Hamas' media office reported that the sons were killed by a strike on their car while they were driving in Al-Shati refugee camp west of Gaza City. Three of Haniyeh's grandchildren were also killed in the raid, Hamas said.

Later in the day, Israel officially confirmed the attack.

"An aircraft struck three Hamas military operatives that conducted terrorist activity in the central Gaza Strip," Israel's Shin Bet security service and the Israel Defense Forces (IDF) said in a joint statement.

According to the statement, the three sons who were killed are Amir Haniyeh, Mohammad Haniyeh, and Hazem Haniyeh.

The IDF added in the statement that it is "aware of claims that other relatives of Haniyeh were harmed, among them a minor. This information is not verified by the IDF."

Haniyeh said in an interview with Al Jazeera TV after the attack that the killing of his sons would not affect Hamas' demands in Gaza ceasefire negotiations.

Haniyeh, the 61-year-old Hamas leader, is based in Qatar.