President Joe Biden ’s administration is “very, very” worried by Iran’s progress toward nuclear weapons-grade uranium, a top diplomat acknowledged Wednesday.

“It is very, very worrisome,” Ambassador Linda Thomas-Greenfield, who leads the U.S. mission to the United Nations , told House lawmakers. “And I know that we're looking at how we respond.”

U.N. nuclear watchdogs have detected uranium enriched to 83.7%, according to a new confidential report from the International Atomic Energy Agency that Greenfield confirmed she has seen. That finding raised the question on Capitol Hill of whether Biden will intervene in time to thwart Tehran’s nuclear ambitions.

“Given Iran’s previous obstructions to U.N. and IAEA nuclear inspections, how can we be sure Iran is not intentionally increasing its enrichment efforts to use for nuclear weapons?” Rep. Hal Rogers (R-KY), the longest-serving member of the House, asked the ambassador. “It’s no longer time to talk. It’s time to act.”

The U.N. ambassador throughout the exchange tried to allay Rogers’s concern without signaling any specific plan or timetable. “I won’t project when and how the administration will respond, but I know that the administration is prepared to,” she said.

The U.S. response to the Iranian nuclear program has been characterized by a divide between both Republicans and Democrats as well as between U.S. allies in the Middle East and Europe. Democrats and Europeans embraced Barack Obama’s 2015 Iran nuclear deal as an effective mechanism to constrain the weapons program, while Republicans and leaders such as Israeli Prime Minister Benjamin Netanyahu denounced the pact for allowing Iran to keep its enrichment program.

Iran’s military support for Russia's war in Ukraine has presented Netanyahu with an opportunity to try to persuade U.S. and European officials to adopt a more confrontational posture toward Tehran, despite his hesitance to join the trans-Atlantic allies in arming Ukraine .

“Iran is not just Israel’s problem. And I’m not just talking about the nuclear threat,” Israeli Maj. Gen. Oded Basiuk said Wednesday. “In the last month, Iran tried twice to attack vessels in the Arabian Sea and failed, and it did so using drones, which we also see being used in the Ukraine-Russia war.”

Such aggressive behavior has helped to put negotiations about the rehabilitation of the Iran nuclear deal, which the U.S. exited in 2018 under Donald Trump, “on ice” although they are not ready to abandon hope of restoring the pact at some point, despite the progress of Tehran’s nuclear program in recent years.

“Back in 2018 ... it would have taken Iran about twelve months to produce one bomb's worth of fissile material; now, it would take about twelve days,” Defense Department Undersecretary Colin Kahl told House lawmakers Tuesday. “And so I think there is still the view that if you can resolve this issue diplomatically and put constraints back on their nuclear program, it is better than the other options.”

Rogers suggested that Iranian officials have approached too close to the nuclear threshold for U.S. officials to place their confidence in diplomatic options.“They’re within inches of having the bomb,” he argued. “It’s time,” Rogers told Thomas-Greenfield.

Thomas-Greenfield reiterated Biden’s pledge not to allow the regime to acquire nuclear weapons . “We have not lost sight of what they are doing on the nuclear side,” she said. “I again stress that the president has been clear that we will not stand by and allow them to gain nuclear capabilities.”