May 7 (Reuters) – An Israeli air strike has killed the son of Hamas’ chief negotiator in U.S.-mediated talks over Gaza’s future, a senior Hamas official said on Thursday, as leaders of ​the militant group held talks in Cairo aimed at safeguarding their truce with Israel.

Azzam ‌Al-Hayya, son of Khalil Al-Hayya, succumbed to his injuries on Thursday after being struck in an Israeli attack on Wednesday night, said senior Hamas official Basim Naim. He is the fourth son of Hamas’ exiled Gaza chief to have been ​killed in Israeli attacks.

The Israeli military did not respond to a request for comment.

Hayya, who has seven children, has ⁠survived multiple Israeli attempts to kill him. An Israeli strike in Doha last year targeting Hamas ​leadership killed his son, though Hayya survived. Two other sons were killed in past Israeli attempts on ​his life, in Gaza strikes in 2008 and 2014.

Speaking to Al Jazeera after the attack on Wednesday night, before his son’s death was announced, Hayya accused Israel of trying to undermine mediators’ efforts to push ahead with U.S. President Donald ​Trump’s Gaza plan, overseen by his so-called “Board of Peace”.

“These Zionist attacks and violations clearly indicate that ​the occupation does not want to abide by a ceasefire or by the first phase,” said Hayya.

The violence comes ‌as leaders ⁠of Hamas and other Palestinian factions held talks with regional mediators and the Board of Peace’s lead envoy, Nickolay Mladenov, this week in Cairo, to push Trump’s Gaza plan into its second phase, officials said.

Trump’s Gaza plan, which Israel and Hamas agreed to in October, involves Israeli troops withdrawing from Gaza ​and reconstruction starting as ​Hamas lays down its ⁠weapons.

But Hamas’ disarmament is a sticking point in talks to implement the plan and cement an October ceasefire that halted two years of full-blown war.

A ​Hamas official told Reuters on Wednesday the group told Mladenov it would ​not engage in ⁠serious talks over the implementation of the second phase before Israel concludes obligations stemming from the first phase of the Gaza deal, including a complete halt to attacks.

At least 830 Palestinians have been killed since ⁠the ceasefire ​deal took effect, according to local medics, while Israel says ​militants have killed four of its soldiers over the same period.

Israel says its strikes are aimed at thwarting attempts by Hamas ​and other Palestinian militants to stage attacks against its forces.