"America has entered a crisis of strategic decision-making that looks at the international arena immaturely and adventurously," said parliament speaker Ali Larijani, a key establishment figure, at a conference on the Palestinian situation in Tehran.
"I believe the current US president is not capable of identifying and judging the long-term consequences of his actions," he added.
The United States was due to open its new embassy in Jerusalem -- known as Al-Quds in Iran -- later on Monday amid widespread Palestinian anger and praise from Israelis.
"Spur-of-the-moment and uncalculated actions cannot continue in today's world. Feeblemindness is costly for statesmen and they will eventually have to pay the price," Larijani said.
Iran is a key backer of Palestinian militant groups, including Hamas, and opposition to Israel has been a central tenet of its regime since the 1979 Islamic revolution.
Larijani called for an "immediate reaction" from Palestinians, Islamic countries and the international community -- including boycotts and official complaints to the United Nations.
The US "must not think that such actions... can remain without a response," he said.
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