On Saturday, the UK ambassador in Iran, Rob Macaire, was briefly detained for allegedly organizing and participating in ongoing protests in Tehran. A spokesperson for UK Prime Minister Boris Johnson described the incident as "an unacceptable breach of the Vienna Convention" and called for an investigation.

Iranian Foreign Minister Javad Zarif said on Monday that the UK was "parroting the US line & blindly abetting its terrorist adventurism in our region". Tehran's top diplomat questioned the possible outcomes of the UK policy, recalling that "the last time the UK was dragged along to infamy by the US was in the Iraq war".

Earlier in the day, Iranian government spokesman Ali Rabiei urged the UK government to not interfere with Tehran’s internal affairs. Prior to Rabiei's statement, Hamid Baeidinejad, Iranian ambassador to the UK, demanded that foreign diplomatic personnel avoid taking part in rallies that are not approved by the nation's government.

Rabiei suggested that the UK ambassador's participation in the recent protests in Tehran contradicted the ambassador’s responsibilities and duties.

Macaire tweeted on Sunday that he was not attending protests but acknowledged that he did take part in what he believed at the time was a vigil for victims of the crash of a Ukrainian plane in Iran.

The rallies in which Macaire reportedly took part were said to have been dedicated to the deadly plane crash in Iran that occurred last week, killing all 176 passengers and crew.

A peaceful commemoration, which was purportedly not approved by authorities in the Iran government, resulted in a large rally demanding the resignation and prosecution of those responsible for the Ukrainian Boeing 737-800 plane crash. 

Existing Tensions and the Future of the JCPOA

In a separate tweet, Zarif slammed the 'EU three' countries (E3) that are signatories to the 2015 Iran nuclear deal, officially known as the Joint Comprehensive Plan of Action (JCPOA), for bowing to a "US diktat", noting that the only way to save the landmark agreement is to "fulfill its own obligations".

The JCPOA was signed in 2015 by Iran, China, France, Germany, Russia, the United Kingdom, the United States, and the European Union, and required Iran to scale back its nuclear program and severely downgrade its uranium reserves in exchange for sanction relief. Following the 2016 US presidential elections, the Trump administration in 2018 abandoned the conciliatory policy of the White House toward Iran, withdrawing from the JCPOA and instituting new Iranian petroleum industry sanctions.

On May 8, 2019, the first anniversary of the 2018 White House unilateral withdrawal from the 2015 agreement, Iran announced a gradual reduction of its JCPOA obligations.

On Sunday, in the aftermath of a US drone attack that killed Quds Force top commander Qasem Soleimani, Tehran announced that it would discontinue its remaining JCPOA obligations. The Iranian ambassador to the UN, Majid Takht Ravanchi, noted that despite the JCPOA rollback, Tehran is not interested in building its own nuclear weapons.