Iran is gearing up to retaliate against Israel over the killing of the Hamas political leader in the country, while Israel and the United States are stepping up security cooperation to counter Iranian threats.

Ismail Haniyeh was killed during a visit to Iran last month. Iran blames Israel and has vowed to take revenge.

Iran's state-run television reported on Friday that the commander of the country's Islamic Revolutionary Guard Corps' Quds Force, Ismail Qaani, sent a letter to new Hamas political leader Yahya Sinwar. The Quds Force is an elite unit supporting Hamas and other anti-Israel forces.

In the letter, Qaani reportedly said Iran will undoubtedly inflict harsh punishment on Israel.

Meanwhile, Israeli Defense Minister Yoav Gallant spoke by phone with US Defense Secretary Lloyd Austin to discuss defense assistance.

Israel Defense Forces Chief of the General Staff, Lieutenant General Herzi Halevi, revealed that he conducted a situational assessment with the visiting commander of the US Central Command.