Opposition leaders in Israel blasted Prime Minister Benjamin Netanyahu on Wednesday for firing his defence minister, saying it threatened national security at a time of war.

At a joint news conference in Jerusalem, they accused Netanyahu of putting his own political interests before the country's, following his decision the day before to dismiss Yoav Gallant.

"He had the choice between disgrace and war, and he chose disgrace," said former prime minister Yair Lapid, voicing outrage at the move as Israel faces military pressures on multiple fronts.

"Our soldiers cannot trust him. The citizens of Israel cannot trust him. Yesterday the whole State of Israel saw that', he said of Netanyahu.

Netanyahu's office announced the sacking of Gallant on Tuesday following public differences over the war with Hamas.

"Over the past few months... trust has eroded. In light of this, I decided today to end the term of the defence minister," Netanyahu's office said, adding that foreign minister Israel Katz would take his place, and that Gideon Saar was appointed foreign minister to replace Katz.

Leading opposition figure Benny Gantz, who quit Netanyahu's government in June over its lack of a post-war plan for Gaza, called the timing of the move "absolute security negligence".

"What should our fighters in Lebanon think today, seeing that the minister of defence is fired after he issues conscription orders?" he asked, referring to an order sent on Monday for the conscription of 7,000 ultra-Orthodox individuals, a community historically exempted from military service.

The orders came at a time when Israel is struggling to bolster troop numbers, with ground forces deployed to fight Hamas in the Gaza Strip and Hezbollah in Lebanon.

Meanwhile, thousands of Israelis took to Tel Aviv's streets to protest against Gallant's dismissal on Tuesday night, chanting slogans against Netanyahu and demanding the return of 97 hostages held in Gaza.

For his part, Gallant said in a post on X that Israel's security would remain his life's "mission".

He called on the government to bring home the hostages in Gaza while they were "still alive" and insisted all Israelis of draft age must serve in the military.

Hamas' October 7 attack on Israel resulted in the deaths of 1,206 people, according to a tally of Israeli official figures.

Israel's retaliatory campaign has killed 43,391 people in Gaza, a majority of them civilians, according to Gaza health ministry figures which the United Nations considers to be reliable. (AFP)