Benny Gantz, a centrist member of Israel’s war cabinet, presented Prime Minister Benjamin Netanyahu with an ultimatum on Saturday, saying he would leave the government if it did not soon develop a plan for the future of the war in Gaza.

While Mr. Gantz’s departure would not topple the country’s emergency wartime government, the move would further strain a fragile coalition that has provided Mr. Netanyahu’s far-right government with a boost of international legitimacy, and it would make the prime minister even more reliant on his hard-line partners.

“If you choose the path of zealots, dragging the country into the abyss, we will be forced to leave the government,” Mr. Gantz said in a televised news conference. “We will turn to the people and build a government that will earn the people’s trust.”

Mr. Gantz, who leads the National Unity party, said he would give Mr. Netanyahu until June 8 — three weeks’ time — to develop a plan that would aim to secure the release of hostages taken to Gaza by Hamas-led militants on Oct. 7, address the future governance of the territory, return displaced Israelis to their homes and advance normalization with Saudi Arabia, among other issues.

Mr. Gantz’s ultimatum was the latest sign of pressure building on Mr. Netanyahu to develop a postwar plan. The prime minister is increasingly being squeezed — externally from Israel’s closest ally, the United States, and from within his own War Cabinet — to clarify a strategy for Gaza. Just days earlier, Yoav Gallant, Israel’s defense minister, said the government was charting “a dangerous course” and demanded that Mr. Netanyahu immediately pledge not to establish an Israeli military government in Gaza.

In a response to Mr. Gantz’s ultimatum, Mr. Netanyahu accused the former military chief of staff and a longtime political rival of calling for “Israeli defeat” by effectively allowing Hamas to remain in power.