The US vowed Monday to be “relentless” in countering Iran as sweeping sanctions took effect, but Tehran defiantly promised to stand up to the “bullying” by Washington.

In a teleconference with journalists in the region, Brian H. Hook, US Special Representative for Iran and Senior Policy Adviser to Secretary of State Mike Pompeo said the Trump administration’s goal was zero imports of Iranian oil. “We have prepared for this day for the past six months. A million Iranian barrels of oil per day have been reduced from the market. More than 20 countries that previously imported oil from Iran have stopped” doing so, Hook said. “We will impose maximum economic pressure on Iran until it changes its behaviour.”

His comments came as the Belgium-based SWIFT financial messaging service said on Monday it was suspending some unspecified Iranian banks’ access to its messaging system in the interest of the stability and integrity of the global financial system.

Hook said that European banks will avoid business with Iran as a result of the new sanctions regime. “If you are a European businessman or corporation, and your choice is between doing business with the United States or with Iran, it is the fastest decision you will make,” Hook said.

He added the US was adopting a three-pronged approach to Iran: diplomacy; restoration of deterrence; and standing with the Iranian people. “The Iranian people have suffered 39 years of economic mismanagement. The regime spends money on exporting violence and terror in the Middle East. Iran has given hundreds of millions of dollars to the Al Houthi militia in Yemen; it has spent $4.6 billion on Bashar Al Assad’s regime in Syria; and it gives $700 million a year to Hezbollah. The nuclear deal gave them $100 billion in sanctions relief and $150 billion in cash. The regime spent this on Lebanon, Iraq, Syria, Yemen and on Hezbollah and Hamas,” Hook said.

Iran greeted the re-imposition of sanctions on Monday with air defence drills and an acknowledgement from President Hassan Rouhani the nation faces a “war situation”. “Today, Iran is able to sell its oil and it will sell,” Rouhani vowed Monday.

Rouhani, meanwhile, pledged Iran would overcome the sanctions. “We are in the war situation,” Rouhani said. “We are in the economic war situation. We are confronting a bullying enemy. We have to stand to win.”

He said: “I announce that we will proudly bypass your illegal, unjust sanctions because it’s against international regulations. We are in a situation of economic war, confronting a bullying power. I don’t think that in the history of America, someone has entered the White House who is so against law and international conventions.”

Iranian state television aired footage of air defence systems and anti-aircraft batteries in two-day military manoeuvres underway across a vast stretch of the country’s north. It included surface-to-air missiles shooting down a drone.

The drill was to continue through Tuesday. Iranian army Gen. Habibillah Sayyari said both the national army and the country’s paramilitary Revolutionary Guard were taking part in the exercise.

-With inputs from agencies