The United Nations nuclear watchdog chief said on Monday he is concerned about Israel possibly targeting Iranian nuclear facilities, but that International Atomic Energy Agency (IAEA) inspections of Iranian facilities would resume on Tuesday.

Israel's military chief said on Monday his country would respond to a weekend missile and drone attack by Iran, launched in retaliation for a suspected Israeli airstrike on its embassy compound in Damascus on April 1. This comes amid calls for restraint by allies anxious to avoid an escalation of conflict in the Middle East.

IAEA Director General Rafael Grossi said Iran closed its nuclear facilities on Sunday over "security considerations" and that while they reopened on Monday, he kept IAEA inspectors away "until we see that the situation is completely calm."

"We are going to resume tomorrow," Grossi told reporters in New York. "This has not had an impact on our inspection activity."

When asked about the possibility of an Israel strike on Iranian nuclear facilities, Grossi said: "We are always concerned about this possibility." He urged "extreme restraint." The IAEA regularly inspects Iran's main nuclear facilities like its enrichment plants at Natanz that are at the heart of the country's nuclear program.

Iran says its nuclear program is entirely peaceful, but Western powers accuse Tehran of seeking to make nuclear bombs.