Iran's president Hassan Rouhani said his administration and the country would show a "unified" response to a breach of the 2015 nuclear deal with world powers.
"The world should know that any breach of the deal will face a unified reaction of the Iranian nation and government," Mr Rouhani said during his inauguration for a second term as president.
Iran's state TV reported that more than 130 high-ranking officials from various countries and international organisations attended the ceremony in Tehran. Among them was EU's foreign policy chief Federica Mogherini, who coordinates follow-up of the nuclear deal.
It was the first time in Iran's history that a large number of foreign officials attended a presidential inauguration.
"Those who intend to tear down the deal, should know that they are tearing down their political life," said Mr Rouhani, without elaborating.
US president Donald Trump has repeatedly described the nuclear deal as "bad" and during his campaign vowed to dismantle it.
Mr Trump signed a bill Wednesday that imposes mandatory penalties on those involved in Iran's ballistic missile programme and anyone who does business with them.
It would also apply terrorism sanctions to Iran's prestigious Revolutionary Guard and enforce an arms embargo. Iran has vowed to respond if the bill becomes law.
However, Mr Rouhani said his administration would maintain its "moderate" behaviour in response to any verbal challenge.
"We prefer peace to war and reform to rigidness," he said.
Mr Rouhani, 68, a moderate cleric who secured re-election on May 19, promised that his country would pursue a "path of coexistence and interaction with the world".
He has vowed that in his second term in office, Iran will "insist on constructive engagement with the world more than before".
Mr Rouhani was first elected in 2013 with nearly 51 per cent of the vote.
Iran's supreme leader Ayatollah Ali Khamenei formally endorsed him for his second term as president on Thursday. Mr Rouhani has to announce his new cabinet members to Parliament within 14 days and is expected to do so on Tuesday.