New Delhi, March 18 -- Israel killed two senior Iranian security officials in a major blow to the Islamic Republic's leadership as it faces its greatest test in decades, and Iran responded Wednesday with renewed missile and drone attacks on its Gulf Arab neighbors and Israel.

Ali Larijani, secretary of Iran's Supreme National Security Council, was considered one of the most powerful figures in the country since Supreme Leader Ayatollah Ali Khamenei was killed in an airstrike on the first day of the war. Gen. Gholam Reza Soleimani was the head of the Revolutionary Guard's all-volunteer Basij.

Iran confirmed the killings of the men, who were key to Iran's violent crackdown on protests in January that challenged the theocracy's 47-year rul...