It said they must agree to "fix the bad flaws of the Iran nuclear deal" - which was sealed under President Barack Obama - or he would refuse to extend US sanctions relief on Iran.
Retired US Air Force Lieutenant Colonel Karen Kwiatkowski told Sputnik that Trump's decision to drop Tillerson and replace him with Pompeo, a longtime critic of the nuclear deal, was a triumph for Israel's right wing Likud government and its US political allies.
Trump said in January that the nuclear deal must be "fixed" by May 12 or the United States will walk away.
State Department policy planning chief Brian Hook, who is running the negotiations with Europe, will lead the US delegation to the larger meeting in Austria's capital. USA sanctions will resume unless Trump issues fresh "waivers" to suspend them on May 12. Hook, who Tillerson leaned on heavily for policy advice and direction, could meet separately in Vienna with the Iranian delegation head, Deputy Foreign Minister Abbas Aragchi.
In firing Tillerson on Tuesday, Trump in particular noted his disagreement over the Iran accord.
Such discussions between the USA and Iran have occurred occasionally on the margins of regularly scheduled Iran deal talks.
Prior to the joint commission's meeting, the Iranian envoy said in a tweet that "the U.S., now more than ever, is under pressure and unprecedented isolation in the face of the alliance of all parties [to the deal]".
"Now he has a secretary of state who 100% shares his views on the nature and gravity of the Iranian threat and the fatal flaws of the JCPOA", Dubowitz said in an interview, using the initialism for the deal's official name.
Trump's next deadline to extend some of those concessions is May 12.
As a congressman, Pompeo vociferously denounced the accord when it was struck. This would seriously undercut the Iran's ability to fund terrorist groups or build weapons of mass destruction.
Pompeo may moderate some of his criticisms of the nuclear deal if he becomes secretary.
His stance and position with Trump could give Pompeo leverage with the Europeans that Tillerson never enjoyed.
Citing Tehran Times daily, Xinhua reported the Iranian diplomatic team visiting Vienna for regular talks on the implementation of Iran's nuclear deal would meet other participating sides including the United States officials on Friday, a source close to the Iranian negotiators said on condition of anonymity. However, the president has also proven his willingness to abandon worldwide agreements negotiated by his predecessors and has made clear his opposition to the Iranian government and the deal itself.
USA and European diplomats say they're closer on long-range ballistic missile launches, inspections and new sanctions on Iranian-backed militant groups. He added that without the full commitment of the USA and all parties, it is not possible to imagine the survival of the agreement. Iran maintains that it must have medium-range missiles to defend itself, an argument the Europeans have been sympathetic to. "It may well be the first casualty of Tillerson's ousting will be the end of the Iran deal".
Iranian Foreign Ministry spokesman Bahram Qasemi said Wednesday he backed Trump's acceptance of an apparently surprise invitation to meet North Korean leader Kim Jong Un, with whom the president has feuded throughout the past year.