The US State Department said on Tuesday that it was "too soon to tell" if any progress had been made in restoring the 2015 Iran nuclear deal as talks continue with Tehran. Negotiations resumed in Vienna Monday in a fresh attempt to salvage the landmark agreement, which curtailed Iran's nuclear activities in return for sanctions relief. "There may have been some modest progress," State Department spokesman Ned Price told reporters in Washington. "But it is in some ways too soon to say how substantive that progress may have been. At a minimum any progress, we believe, is falling short of Iran's accelerating nuclear steps and is far too slow." Former US President Donald Trump in 2018 withdrew from the nuclear accord. President Joe Biden supports a return to the agreement but Iran has kept taking steps away from compliance as it presses for sanctions relief. Iran has refused to engage with US officials directly following the Trump administration's withdrawal from the Joint Comprehensive Plan of Action (JCPOA). The Vienna talks began after Biden's election but stopped in June as Iran elected a new conservative government. They resumed in late November with Iran agreeing to keep talking after a brief break. Following the US withdrawal from the JCPOA, the Trump administration enforced sanctions on Iran and claimed it was not abiding by the terms of the deal. The remaining member nations tied to the deal, including Britain, China, France, Germany, Russia and the European Union, advised the US against such action and argued it would weaken the deal. Iran proceeded to further negate the terms of the JCPOA by advancing its nuclear capabilities while simultaneously blocking international access to its program. Tehran has unequivocally called for all sanctions placed on Iran during the Trump administration to be revoked. But given Iran's nuclear advancement, the Biden administration has not yet agreed to lift any sanctions. "The fundamental position as of today has not changed," Price said. "Iran has at best been dragging its feet in the talks while accelerating its nuclear escalations." Price said the US was now assessing terms laid out in December's negotiations and said the US still believes mutual compliance with the JCPOA can be "quickly" realized "if Iran is serious." It is unclear how many more rounds of talks JCPOA member nations will engage in or if a deal can even be struck, but world leaders have routinely warned time is running out. "This negotiation is urgent," negotiators from Britain, France and Germany said in a statement. "We are clear that we are nearing the point where Iran's escalation of its nuclear program will have completely hollowed out the JCPOA," they said. Israel, Iran's arch-enemy, has warned of military options if the Islamic republic's program advances and is suspected in a shadowy campaign that has included the assassination of Tehran's top nuclear scientist. The Biden administration has also warned of a return to pressure if talks fail and Iran pursues its nuclear work. Iran was in compliance with the 2015 deal before Trump's withdrawal but has since taken key steps including stepping up its enrichment of uranium, although it denies that it wants to acquire a nuclear arsenal. On Saturday, Atomic Energy Organization of Iran director Mohammad Eslami said Tehran had no plans to enrich uranium beyond 60 percent, even if the Vienna talks fail. Eslami said the enrichment levels were related to the needs of the country, in remarks published by the Russian news agency RIA Novosti. In response, E3 negotiators said Tuesday that 60 percent enrichment was still "unprecedented for a state without nuclear weapons". Military-grade levels are around 90 percent. "Its increasing 60 percent stockpile is bringing Iran significantly closer to having fissile material, which could be used for nuclear weapons," they said. The United States did not specify areas of progress but Russia -- which is participating along with China and the Europeans -- said a working group had a "useful meeting" on nuclear issues and informal discussions on lifting sanctions. "We observe indisputable progress," Moscow's ambassador to the UN in Vienna, Mikhail Ulyanov, wrote on Twitter. US negotiator Rob Malley is participating indirectly, with European diplomats shuttling between hotels, as Iran refuses direct contact with the United States. Iran's Foreign Minister Hossein Amir-Abdollahian was quoted by state news agency IRNA on Tuesday as saying the negotiations were "on a good track". "With the goodwill and seriousness from the other parties, we can consider (reaching) a quick agreement in the near future," he said. — Agencies