"I urge the US to avoid taking any action that would hinder other parties from continuing to make the agreement work," Johnson told parliament, adding that Britain had "no intention of walking away" from the deal, which remained "vital" to its national security.

"For as long as Britain abides by the agreement... then Britain will remain a party to the JCPOA (Joint Comprehensive Plan of Action," he said.

"It's now up to Washington to come up with concrete proposals."

European leaders and key trading power China have vowed to save the 2015 accord, which lifted sanctions on Iran in return for it halting an alleged nuclear weapons programme and allowing international inspections.

They have also vowed to protect companies operating in the country after President Donald Trump announced Tuesday that as a result of pulling out of the deal the US would reinstate severe sanctions against Tehran.

Trump's national security advisor John Bolton said European firms doing business in Iran now have a six-month deadline to wind up investments or risk American sanctions.

"We will do our utmost to protect UK commercial interests," Johnson told lawmakers when pressed on the potential impact on British firms dealing with Tehran.

The foreign secretary said Britain was aware "Iran is up to all sorts of bad behaviour in the region" but that they were not in violation of the JCPOA.

He added America must now provide fuller details of how it plans to proceed outside the framework.

"It falls to the US administration to spell out their view of the way head," said Johnson, who visited Washington earlier this week and failed to convince Trump to remain inside the nuclear deal.

"President Trump said himself last night that he is committed to finding a new solution and we should hold him to his word," he added.

"We have yet to see the detail of how he intends to do it, but we will certainly be as supportive as we can."

Questioned by several lawmakers on whether the US was considering a military solution to the issue, Johnson insisted "there is no such plan".

"After closely interrogating everybody I could find in the White House, there is no enthusiasm for a military option in the United States," he added.

Prime Minister Theresa May earlier told parliament: "We accept that there are other issues in relation to the behaviour of Iran in the region.

"Those are issues that need to be addressed and we are working with our European and other allies to do just that," she said.

Johnson told lawmakers he expected to meet with EU diplomatic chief Federica Mogherini next week to discuss the bloc's next steps on Iran.