The nuclear deal reached between Iran and the six world powers of Britain, China, France, Russia and the United States plus Germany in July 2015 resulted in the removal of worldwide and western sanctions against Iran in return for the strict monitoring of the country's nuclear program.
Johnson said: "The UK has always been clear: the Iran nuclear deal is a crucial agreement that makes the world safer".
"We greatly value the JCPOA, the nuclear deal with Iran, we think it is a considerable diplomatic accomplishment, it's a way of stopping Iran from acquiring nuclear weapons and Iran is in compliance with this agreement according to the International Atomic Energy Agency", Johnson said.
"We will not remain silent as the Iranian dictatorship represses the basic rights of its citizens and will hold Iran's leaders accountable for any violations", White House press secretary Sarah Sanders said.
French Foreign Minister Jean-Yves Le Drian is to raise Paris' concerns about the deal as well as its ballistic missile program while also seeking to keep dialogue open with Iran, a spokesman told journalists.
"All parties should uphold the deal", he said, speaking through a translator.
President Donald Trump is expected to continue sanctions waivers that accompanied the accord in a decision to be made later Thursday despite his refusal to certify Iran's compliance with the pact late previous year.
"It's about the U.S.'s relationship with its longstanding European Union partners", argues Trita Parsi, who heads the National Iranian American Council and was an outspoken supporter of the Obama administration's pursuit of the nuclear deal.
Trump, who in October refused to certify Iran was complying with the deal but stopped short of withdrawing from it, is expected to decide on Friday whether to extend waivers on nuclear-related sanctions against Tehran.
If Trump did waive the sanctions, one official said, the administration would nevertheless impose new, targeted measure on Iranian businesses and people.
His decision is also further complicated by recent mass anti-government protests in Iran, made up mostly of youths complaining of economic hardship.
Iranian Foreign Minister Mohammed Javad Zarif, who traveled to Moscow on Wednesday to seek Russian support, criticized what he called Washington's "destructive policy", Agence France-Presse (AFP) reported.
"The unity of the worldwide community is essential to preserve a deal that is working, that is making the world safer and that is preventing potential nuclear arms race in the region". On Wednesday, a top Iranian nuclear official warned the country could ramp up enrichment beyond pre-2015 levels if the deal is scrapped.
"Everyone agrees it is imperative that ALL live up to their obligations under JCPOA".
The IAEA is responsible for overseeing Iran's compliance with the deal's nuclear restrictions.