Tehran will "use all available tools" to respond to Israel's weekend attack on military targets in Iran, Iranian Foreign Ministry spokesperson Esmaeil Baghaei said on Monday.
Iran previously played down Israel's air attack on Saturday, saying it caused only limited damage, while US President Joe Biden called for a halt to escalation that has raised fears of an all-out conflagration in the Middle East.
Speaking at a weekly televised news conference, Baghaei said: "(Iran) will use all available tools to deliver a definite and effective response to the Zionist regime (Israel)".
The nature of Iran's response depends on the nature of the Israeli attack, Baghaei added, without elaborating.
Iran's Supreme Leader Ayatollah Ali Khamenei said on Sunday that Iranian officials should determine how best to demonstrate Iran's power to Israel, adding that the Isreli attack should "neither be downplayed nor exaggerated".
Scores of Israeli jets completed three waves of strikes before dawn on Saturday against missile factories and other sites near Tehran and in western Iran, Israel's military said.
The heavily armed arch-enemies have engaged in a cycle of retaliatory moves against each other for months, with Saturday's strike coming after an Iranian missile barrage on October 1, much of which Israel said was downed by its air defences.
Iran backs Hezbollah, which is engaged in heavy fighting with Israeli forces in Lebanon, and also the Palestinian group Hamas, which is battling Israel in the Gaza Strip.
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