“If the US wants to take a hostile position regarding an international agreement which is approved by the UN Security Council...
they will oppose not just Iran but the whole world,” Rouhani said at a cabinet meeting shown on state television.
“It will be absolutely clear which is the lawless government.
It will be clear which country is respected by the nations of the world and global public opinion,” he added.
Trump is due to deliver a speech as early as today outlining a tougher line on Iran, and is expected to say he will no longer certify the 2015 nuclear deal as required every three months.
The US Congress would then have 60 days to decide on whether to reimpose sanctions, effectively pulling out of the nuclear agreement.
Other parties to the deal — Britain, France, Germany, China, Russia and the European Union — have all voiced staunch support for it, saying Iran has stuck to its commitments to curb its nuclear programme.
The nuclear deal “is a test for all governments,” Rouhani said.
“Whenever we have committed ourselves, we have stood by our commitments to the end.
This is an honour for us.”
Rouhani also took aim at reports that the US may declare Iran’s elite Revolutionary Guards a terrorist organisation.
“This will be a mistake. The Revolutionary Guards are not just a military unit, the Revolutionary Guards are in the hearts of the people,” he said.
He said Trump was “clearly upset” over the Guards’ military successes against the Islamic State group in Syria and Iraq.
“OK, if you want to keep Daesh (the Islamic State group) in this region for 20 years and use it as a tool, then OK, it is your right to be angry with the Revolutionary Guards. Because the Revolutionary Guards, by their planning, and support for the nations of Iraq, Syria and Lebanon have humiliated Daesh,” Rouhani said.
Threats from Washington have also brought a show of unity from Iran’s often fractious institutions.
“We are one society. We are all Iran. There are no differences among our factions in confronting our enemies’ conspiracies,” Rouhani said.
“The current US president has created a situation where Iran is more integrated than ever, more unanimous, more united.”
Earlier in the day, Foreign Minister Mohamed Javad Zarif gave a closed door briefing to parliament on possible responses to Trump’s speech.