During his first trip to the Middle East since taking office, President Joe Biden announced that the US will use force as a “last resort” to prevent Iran from obtaining nuclear weapons. While such a warning is a step in the right direction, it is not adequate given that the Iranian regime is not taking the Biden administration seriously. If there was a real fear in Tehran of US military action in response to the continuation of its nuclear program, the regime would most likely halt its activities. After the US invaded Iraq in 2003, for example, and the Bush administration issued warnings to Tehran about its nuclear program, the Iranian regime took those warnings seriously and immediately halted its nuclear research. It also rushed to offer Washington a deal that reportedly would have curtailed its nuclear program. But a thorough examination of the latest statements by Iranian leaders and state-controlled media outlets reveal that the theocratic establishment does not respect President Biden’s warnings. If the Iranian regime is to take the Biden administration seriously, the president ought to give Tehran a clear ultimatum and deadline to halt its nuclear program or else the US will deploy forces to prevent Iran becoming a nuclear nation. Unfortunately, since Biden assumed office in January 2021, the Iranian regime has been buying itself time to make major advancements in its controversial nuclear research. At the same time as several rounds of negotiations with the P5+1 world powers (China, France, Russia, the UK, the US and Germany) have been taking place, Tehran has clearly succeeded in significantly speeding up its nuclear program, conducting uranium research, development and production, and adding additional centrifuges. As a result, uranium enrichment levels have increased from 20 percent to 60 percent, a short technical step away from the 90 percent purity required for a nuclear weapon. In November, the Institute for Science and International Security warned: “Iran has enough enriched uranium hexafluoride in the form of near 20 and 60 percent-enriched uranium to produce enough weapon-grade uranium, taken here as 25 kg, for a single nuclear weapon in as little as three weeks. It could do so without using any of its stock of uranium enriched up to 5 percent as feedstock. The growth of Iran’s stocks of near 20 and 60 percent-enriched uranium has dangerously reduced breakout timelines.” If Iran is to take Biden and his administration seriously, the president must deliver an ultimatum and set a clear deadline for the suspension of nuclear research, encourage the UN to reimpose its sanctions, and hold those who violate the sanctions accountable. Dr. Majid Rafizadeh Biden ought to deliver an ultimatum to the Iranian regime demanding cooperation with the International Atomic Energy Agency, the UN’s nuclear watchdog, and answers to the agency’s critical questions about the military dimension of Tehran’s nuclear program. The Iranian regime continues to refuse to answer IAEA questions about uranium particles found at three undeclared nuclear sites. The UN agency last month said that the Iranian regime “has not provided explanations that are technically credible in relation to the agency’s findings at those locations … The agency remains ready to engage without delay with Iran to resolve all of these matters.” Meanwhile Tehran continues to expand its nuclear program and has switched off several UN surveillance cameras. By doing so the regime is effectively preventing the IAEA from monitoring its nuclear activities, including uranium enrichment and the use of centrifuges. If the regime is to take the US seriously, Biden must give it a clear date by which to comply with the IAEA or else UN sanctions will be restored. These critical and crippling sanctions were lifted in 2015 following the signing of the Joint Comprehensive Plan of Action, also known as the Iran nuclear deal. According to the agreement, any signatory can trigger a 30-day countdown to a “snapback” that would restore all of the UN sanctions on Iran, including an arms embargo, if Tehran is found to be failing to meet its obligations under the deal. In addition, the Biden administration must warn and hold accountable those who are violating existing sanctions and helping Tehran circumvent them. Since Biden took office, Iranian oil exports have been on the rise. During the previous US administration, they were significantly reduced to between 100,000 and 200,000 barrels a day. The country is currently exporting more than 1 million barrels a day, about 700,000-800,000 of which go to China. “Oil sales have doubled,” Iran’s hard-line President Ebrahim Raisi recently boasted. “We are not worried about oil sales.” Tehran’s major source of revenue is oil exports. In addition to China it is also shipping considerable amounts of oil to Venezuela, without either country fearing repercussions from Washington. According to a Reuters report on June 13, an Iranian-flagged tanker that was carrying nearly a million barrels of crude “arrived in Venezuelan waters over the weekend, according to a shipping document seen by Reuters.” From the perspective of Iran’s leaders, therefore, Biden’s latest announcement that force will be used as “last resort” is nothing more than a hollow collection of words. If Iran is to take Biden and his administration seriously, the president must deliver an ultimatum and set a clear deadline for the suspension of nuclear research, encourage the UN to reimpose its sanctions, and hold those who violate the sanctions accountable. • Dr. Majid Rafizadeh is a Harvard-educated Iranian-American political scientist. Twitter: @Dr_Rafizadeh