In this file photo, Brian Hook, US special representative for Iran, speaks at the Iranian Materiel Display at Joint Base Anacostia-Bolling in Washington. (PHOTO / AP)

The top US envoy for Iran, Brian Hook, is leaving his post and US special representative for Venezuela, Elliott Abrams, will add Iran to his role “following a transition period” with Hook, Secretary of State Mike Pompeo said on Thursday.

Hook’s surprise departure comes at a critical time when Washington has been intensely lobbying at the United Nations to extend an arms embargo on Iran and as the UN Security Council prepares to hold a vote on the US resolution next week.

“We’re going to continue to make the case for this,” Hook told reporters on Thursday morning, hours before his departure was announced. “We hope that the council can find a way.”

A senior administration official said the transition would take a couple of weeks and Abrams was expected to retain both the Iran and Venezuela roles for the remainder of President Donald Trump’s term.

Hook’s surprise departure comes at a critical time when Washington has been intensely lobbying at the United Nations to extend an arms embargo on Iran and as the UN Security Council prepares to hold a vote on the US resolution next week

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Pompeo did not give a reason for the change but wrote in a tweet that Hook was moving on to the private sector. He described him as a “trusted adviser and a good friend” who had achieved “historic results” in countering Tehran and securing the release of US citizens detained by Iran.

Hook, 52, was appointed to the top Iran role at the State Department in late 2018 and has been instrumental in Washington’s intensifying pressure campaign on Tehran after Trump pulled out of the 2015 nuclear deal between Iran and the world powers.

Opponents criticized Hook and the administration for overly harsh and indiscriminate sanctions, which they said were hurting ordinary Iranians and failing to change the behavior of the Iranian government.

Hook’s departure “does not concern us and is not something we consider as a game-changer,” Alireza Miryousefi, spokesman for Iran’s mission to the United Nations in New York, told Reuters.

“The so-called ‘maximum pressure’ campaign waged by the US government has failed,” he said. “Iran is not on its knees, and will not do so regardless of who is in charge of implementing this bankrupt policy.”

The US bid at the Security Council to extend the arms embargo is a key test that some diplomats say will likely fail as it lacks the necessary support, and veto powers Russia and China have already signaled their opposition.

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If the United States is unsuccessful in its bid, it has threatened to trigger a return of all UN sanctions under a process known as snapback. Some diplomats have suggested Washington will likely start the snapback process, which could take up to 30 days, by the end of August.

Abrams, 72, a Republican foreign policy veteran, was named US special representative for Venezuela in January 2019 and has led a hard-line approach aimed at ousting Venezuelan President Nicolas Maduro.

US officials have said privately that Trump has been frustrated by the failure to remove Maduro, who retains the support of the Venezuelan military, as well as Russia, China, Cuba and Iran.

Abrams has recently been dealing with US concerns about a growing alliance between Iran and Venezuela, both OPEC members under heavy US sanctions. Iran in recent months has sent fuel tankers to gasoline-short Venezuela, drawing US ire.