It appears that the negotiations between Iran and the US on the future of the nuclear accords are being carried out at a very careful pace. According to assessments, Iran's refusal is a result of its precondition that talks include some easing of the economic sanctions on Iran, but the US has yet to agree to such a step.
Recently it was reported that Iran and South Korea reached some sort of agreement regarding Iranian funds being held by Seoul. Any such agreement is supposed to be approved by the US, even if it is done secretly. For the White House, the release of the funds in Seoul to Iran could be considered as an easing of the sanctions by proxy, so neither side loses face.
Furthermore, the US recently released its intelligence report on the involvement of the Saudi crown prince in the murder of journalist Jamal Khashoggi at the Saudi embassy in Turkey in 2018. It should be mentioned that the journalist was drawn to the embassy, where he was dismembered, using a "honey trap" set by Saudi intelligence. Well, according to the report that was published, private jets of the crown prince flew the hit squad responsible for the journalist's murder. Also, the Americans came to the conclusion that the crown prince personally approved the murder.
The US also decided to prevent Saudi Arabia from receiving American weapons used by the Saudis in the war in Yemen. This was done under the pretense of violation of human rights. In Yemen, the Houthi militia is directed and armed by Tehran. The militia operates against Saudi targets using missiles and drones, and also against targets of the central government in Yemen.
The weakening of Saudi Arabia during secret negotiations between the US and Iran is a signal to Iran that the US is apparently ready to be flexible, but not in terms of the sanctions. Not yet. If the US drops the sanctions, the world will perceive the US as weak, and it is doubtful that this is what Biden is looking for at the beginning of his term in office. Biden recently chose to carry out a pinpoint attack against an Iranian militia base on the Syria-Iraq border in order to show that he is not a "sucker". The attack was in response to the bombing of an American base in Iraq. Biden's action was similar to the attack against Syrian targets that Trump carried out at the beginning of his term.
"While we are disappointed at Iran's response, we remain ready to reengage in meaningful diplomacy to achieve a mutual return to compliance with JCPOA (Joint Comprehensive Plan of Action) commitments," the White House spokesperson said regarding the Iranian rejection of talks.