British Prime Minister Theresa May reaffirms UK commitment to Iran nuclear deal in call with US President Donald Trump

Britain's Prime Minister Theresa May leaves 10 Downing Street in central London on September 6, 2017. (Photo by AFP)

British Prime Minister Theresa May has reaffirmed London’s commitment to the Iran nuclear agreement and called on Washington to remain committed to the landmark deal alongside other European signatories.

The British premier made the plea in a telephone conversation with US President Donald Trump on Tuesday.

"The (prime minister) reaffirmed the UK's strong commitment to the deal alongside our European partners, saying it was vitally important for regional security," a statement from May's office said.

"(The prime minister) stressed that it was important that the deal was carefully monitored and properly enforced," it added.

In a tweet on Tuesday, Foreign Secretary Boris Johnson also said he had spoken with his Iranian counterpart, Mohammad Javad Zarif, and reiterated that the UK was “committed" to the deal.

Trump has cast doubt on the future of the US commitment to the accord, known as the Joint Comprehensive Plan of Action (JCPOA), which sought to put limitations on Tehran's nuclear program in exchange for the removal of nuclear-related sanctions.

The US president recently criticized the deal as an "embarrassment," to the United States and "the worst deal ever negotiated."

Britain and the US are two of the signatories to the deal, along with Iran, China, France, Russia, Germany and the European Union. China, Russia and the European states have already expressed their continued support for the agreement.

Iran and the five permanent members of the United Nations Security Council plus Germany signed the nuclear accord in July 2015 and started implementing it in January 2016.

Since the JCPOA Implementation Day, the International Atomic Energy Agency (IAEA) has been verifying Iran’s compliance with its nuclear-related commitments consistently.

While the Trump administration has twice certified Iranian compliance with the deal in notifications to the US Congress under an American law, the White House has indicated that a third verification — early next week — would not be offered.

Trump’s failure to certify the nuclear agreement on October 15 would trigger a 60-day period, during which the US Congress would have to decide whether to violate the deal by re-imposing anti-Iran sanctions.