Iran's President Hassan Rouhani said US sanctions were "economic terrorism", as he sought to foster a united front from visiting regional officials on Saturday.
Washington has reimposed an oil embargo and other damaging sanctions on Iran since pulling out in May from a landmark 2015 nuclear deal between Tehran and major powers.
"America's unjust and illegal sanctions against the honourable nation of Iran have targeted our nation in a clear instance of terrorism," Rouhani said in a televised speech.
He was speaking at a conference on terrorism and regional cooperation attended by parliament speakers from Afghanistan, China, Pakistan, Russia and Turkey.
"We are facing an all-out assault which is not only threatening our independence and identity but also is bent on breaking our longstanding ties," he added.
Rouhani drew parallels with the sanctions and other pressure faced by the countries attending the conference.
"When they put pressure on China's trade, we are all harmed... By punishing Turkey, we are all punished. Any time they threaten Russia, we too consider our security to be endangered," he said.
"When they impose sanctions on Iran, they deprive all of us of the benefits of international trade, energy security and sustainable development. And in fact, they impose sanctions on everyone. We are here to say that we don't intend to tolerate such insolence." Rouhani also warned Europe - which has strongly objected to the US withdrawal from the nuclear deal - that much is at stake in its efforts to bypass US sanctions and maintain trade with Iran.
"They should know that by sanctioning Iran, they would harm our ability to fight drugs and terrorism," Rouhani said, referring to Iran's efforts to combat smuggling, particularly from Afghanistan.
The European Union is working on a payment system, known as the "special purpose vehicle", to keep money flowing into Iran, but has struggled to find a host since many countries fear repercussions from the Trump administration.
The conference in Tehran was the second regional meeting on terrorism - the first was held last December in Islamabad.