GAZA - Three sons of Ismail Haniyeh, the head of the Hamas Political Bureau, along with his four 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 the Al-Shati refugee camp west of Gaza City. Four of Haniyeh's grandchildren, three girls and a boy, were also killed in the attack, Hamas said.

Later in the day, Israel officially confirmed the attack.

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

"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 were Amir Haniyeh, Mohammad Haniyeh, and Hazem Haniyeh.

The IDF said in the statement that it is "aware of claims that other relatives of Haniyeh were harmed, among them a minor”, but added that the 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.

"The blood of my sons is not dearer than the blood of our people," said Haniyeh, who has 13 sons and daughters according to Hamas sources.

The three sons and four grandchildren were making family visits during the first day of the Muslim Eid al-Fitr holiday in Shati, their home refugee camp in Gaza City, according to relatives.

Haniyeh's eldest son confirmed in a Facebook post that his three brothers were killed. "Thanks to God who honored us by the martyrdom of my brothers, Hazem, Amir and Mohammad and their children," wrote Abdel-Salam Haniyeh.

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

With Reuters inputs