Punitive measures reimposed by Donald Trump in the wake of his withdrawal from an international nuclear agreement with Iran came into force today.
Tehran had vowed to smash the sanctions which target the Islamic republic’s vital oil, shipping, insurance, energy and banking sectors.
Mr Zarif said: “Today, US defied UN top court and Security Council by reimposing sanctions on Iran that target ordinary people.
“But US bullying is backfiring. The US – and not Iran – is isolated.”
His comments came after the UK suggested it was against Mr Trump’s decision to reointroduce the sanctions.
A Downing Street spokesman said: “We regret the reimposition of sanctions by the US.
“We continue to believe that the Iran nuclear deal makes the world a safer place and our position remains that as long as Iran continues to meet its obligations under the deal by respecting strict limits on its nuclear activity, we will be committed to it too.
“As such we continue to fully support expanding our trade relationship with Iran and encourage UK businesses to take advantage of commercial opportunities that arise.”
Iranian president Hassan Rouhani earlier vowed to “confront a bullying power”.
He said: “America wanted to cut to zero Iran’s oil sales but we will continue to sell our oil to break sanctions.
“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.”
Mr Trump’s Secretary of State Mike Pompeo has defended the sanctions and heralded them as the “toughest” ever put in place on the country.
Thousands of Iranian students chanted “death to America” on the eve of the sanctions.
US flags, an effigy on Uncle Sam and pictures of Mr Trump were set on fire in images broadcast on state TV.
The Iran nuclear deal was drawn up by the Obama administration and was agreed to by the UK, Russia, France, China, Germany and the EU.