The Israeli army said Sunday it was calling in nearly 100,000 reservists to join its war against Iran.

"The IDF is preparing to call up around 100,000 reservists and is raising its level of readiness on the various fronts as part of Operation 'Roaring Lion'," the military said in a statement, using the name Israel has given to its campaign against Iran which was launched in coordination with the United States on Saturday.

Meanwhile, Israeli Prime Minister Benjamin Netanyahu has announced a further intensification of military attacks on Tehran.

The Israeli army is already attacking with "increasing force" in the heart of the Iranian capital, Netanyahu said in a video message released on Sunday. This force will intensify further in the coming days, he said.

He said he had given the order to continue the offensive following a meeting with Defence Minister Israel Katz, Chief of General Staff Eyal Zamir and the head of the foreign intelligence service Mossad, David Barnea.

Netanyahu said that Israel was deploying the full force of the army "as never before." The aim, he said, was to "secure our survival and our future."

He emphasized that Israel's close cooperation with the U.S. in the joint attacks against Iran would make it possible to do what he had been hoping for 40 years: "To deal a decisive blow to the terror regime."

The U.S. and Israel launched an attack on Iran on Saturday, killing several top officials, including Supreme Leader Ayatollah Ali Khamenei. Tehran retaliated with drone and missile strikes that hit several Gulf countries.

Israel and the U.S. launched a similar attack on Iran last June, triggering a 12-day war before a ceasefire was announced.