United Nations�Secretary General�Antonio Guterres says he does not expect an "immediate" revival of a 2015 multilateral nuclear agreement signed between Iran and world powers that the US unilaterally�left three years later.

The UN chief made the remarks during a Thursday presser, hailing the Joint Comprehensive Plan of Action (JCPOA), as the agreement is officially known,�as �a big diplomatic victory.�

�I believe that everyone, all those who entered the JCPOA and other interested parties must work together to reduce uncertainties, to face difficulties and obstacles,� Guterres said.

The deal was initially signed between Iran and six major world states � the US, Germany, France, Britain, Russia and China � in 2015 and was ratified in the form of UN Security Council Resolution 2231 shortly afterwards.

However, the US under former president Donald Trump unilaterally pulled out of the JCPOA in May 2018 and reinstated the anti-Iran sanctions that had been lifted by the deal.

The Trump administration also launched what it called a maximum pressure campaign against Iran, targeting the Iranian nation with the �toughest ever� restrictive measures.

New US President Joe Biden, who was vice president when the deal was signed during the Obama administration, has said he hopes to return Washington to the deal. But new US Secretary of State Antony Blinken said Wednesday the US will only return to the nuclear deal once Tehran honors its nuclear commitments.

In reaction to the latest remarks by his American counterpart, Iranian Foreign Minister Mohammad Javad Zarif said on Thursday that due to the US various violations of the JCPOA, it is the United States that must take the first step to prove its commitment to the accord.