Iran's supreme leader on Wednesday refused to heed US President Donald Trump's call for an unconditional surrender.
Ayatollah Ali Khamenei made his first public remarks since Friday in a statement that was read live on Iranian TV by a presenter.
"Intelligent people who know Iran, the Iranian nation, and its history will never speak to this nation in threatening language because the Iranian nation will not surrender," the statement on Wednesday said.
"The Americans should know that any US military intervention will undoubtedly be accompanied by irreparable damage," it added.
Iran's UN ambassador warns of response 'without restraint' to Israeli strikes
Iran's ambassador to the United Nations, Ali Bahreini, said the country would "respond strongly" to Israel's "aggression" as well as to the United States, should it join the hostilities.
"We will not show any reluctance in defending our people, security and land," he told reporters in Geneva. "We will respond seriously and strongly, without restraint."
Bahreini accused the United States of being "complicit in what Israel is doing."
"We have given a message to the United States that we will respond very firmly and will stop the aggression by anybody — including the United States," he said
Bahreini also said Israeli strikes on nuclear sites were an act of "war against humanity."
"The deliberate targeting of Iran's nuclear facilities not only constitutes a grave violation of international law and UN Charter but also risks exposition of all people in our neighborhood to possible hazardous leak," he said.
"This is not an act of war against our country," he said. "It is war against humanity."
Iran maintains that its nuclear program is for civilian purposes. Israel and the United States accuse Iran of working toward a nuclear weapon.
The comments come as thousands flee Tehran and other major cities as Israel and Iran continuing launching strikes on one another.
US President Donald Trump has called for Tehran's unconditional surrender.
