Israel's military said it targeted and killed a Hamas cell leader posing as an Al Jazeera journalist in an airstrike on Gaza City on Sunday, a claim condemned by the Qatari broadcaster.

Anas Al Sharif was among a group of four Al Jazeera journalists and an assistant who died in a strike on a tent near Shifa Hospital in eastern Gaza City, Gaza officials and Al Jazeera said. An official at the hospital said there were seven people killed in the strike.

"Anas Al Sharif served as the head of a terrorist cell in the Hamas terrorist organisation and was responsible for advancing rocket attacks against Israeli civilians and IDF (Israeli) troops," the Israeli military said in a statement, citing intelligence and documents found in Gaza as evidence.

Palestinian militant group Hamas, which runs Gaza, said the killing may signal the start of an Israeli offensive. "The assassination of journalists and the intimidation of those who remain paves the way for a major crime that the occupation is planning to commit in Gaza City," Hamas said in a statement.

Palestinian journalists' groups and Al Jazeera denounced the killings. The other journalists killed were Mohammed Qreiqeh, Ibrahim Zaher and Mohammed Noufal, Al Jazeera said.

Calling Al Sharif "one of Gaza's bravest journalists," Al Jazeera said the attack "is a desperate attempt to silence voices in anticipation of the occupation of Gaza."

Israeli Prime Minister Benjamin Netanyahu has said he would launch a new offensive to take control of Gaza, where a hunger crisis is escalating after 3-1/2 years of war.

"Anas Al Sharif and his colleagues were among the last remaining voices in Gaza conveying the tragic reality to the world," Al Jazeera said.

A press freedom group and a UN expert previously warned that Al Sharif's life was in danger due to his reporting from Gaza. U.N. Special Rapporteur Irene Khan said last month Israel's claims against him were unsubstantiated.

In July, the Committee to Protect Journalists urged the international community to protect Al Sharif.