WASHINGTON — A last-minute effort by European powers to persuade Iran not to breach limits on its stockpile of nuclear fuel ended inconclusively on Friday, with the Iranians saying that Britain, France and Germany had made only modest progress in developing a system to get around tight American sanctions on trade with Tehran.
As he left the talks in Vienna, Abbas Araghchi, the Iranian deputy foreign minister, said he expected Iran would go ahead with its plan to break the ceiling on how much low-enriched uranium it was allowed to possess. That breach could come as early as this weekend, potentially setting off another confrontation with the Trump administration, after a week of recriminations and military threats following the downing of an American drone and attacks on tankers.
“It is still not enough, and it is still not meeting Iran’s expectations,” Mr. Araghchi told reporters, according to news reports from Vienna. Any decision on whether to break out of the limits “will be made in Tehran,” he said, hinting that it was possible that further steps to violate the terms of the agreement, scheduled for July 7, might be delayed.
The limits on nuclear fuel were part of a 2015 accord negotiated with Iran by the Obama administration and other big countries, including Russia and China. The deal put strict limits on Iran’s nuclear activities in return for the easing of sanctions. President Trump ended the participation of the United States in the accord last year, saying it did not do enough to assure that Iran could never possess a nuclear weapon or to thwart Iranian aggression in the region.
Iran initially continued to abide by the deal’s terms even after Mr. Trump pulled out, and its threats now to break out of the accord amount to a search for leverage by the government of President Hassan Rouhani. By remaining in compliance with the agreement, Iran hoped to split the Europeans, Chinese and Russians from the United States.
Eager to keep the deal’s main provisions intact, the Europeans have been holding out the possibility of a deal that would allow limited trade with Iran by setting up a barter system to sidestep the American sanctions. But the barter system has taken a long time to come together, and Mr. Rouhani’s government bet that if it moved toward renouncing the nuclear accord, it would force Europe into action.
Breaking the stockpile limit would not, by itself, give Iran enough fuel to produce a nuclear weapon. But the European participants in the 2015 agreement have been urging the Iranians not to dispense with the accord, for fear that the Trump administration might react with a military or cyberstrike against the Iranians.
During talks in Vienna, the Europeans and Iranians were working on details of establishing a barter-trading system, called Instex, that was designed to route around the American sanctions against Iran. But the Europeans have been describing their plans for a year, and declared Friday that the system was just beginning to work — even though it is widely acknowledged that the system would never be robust enough to make up the oil revenue lost to Iran from the United States sanctions.
The United States’ special envoy for Iran, Brian H. Hook, said this week that the sanctions have already cost Iran more than $50 billion.
International nuclear inspectors say Iran is on the cusp of exceeding the stockpile limit. The Trump administration’s position has been that while Washington was free to renounce the agreement, Iran was bound to remain inside it.
Should Iran decide to break out of the agreement in coming days, it will create a major decision point for the United States and Europeans. Mr. Trump’s hard-line advisers, including John R. Bolton, the national security adviser, have long called for a permanent dismantlement of Iran’s nuclear facilities, by military action if necessary.
The Europeans have, until now, blamed Washington for the crisis, though some European officials say that if Iran violated the limits, it may force them to start a process to “snap back” sanctions, under steps laid out in the 2015 document.
Some Iranian officials have gone further in recent weeks, suggesting that Iran might exit the Nuclear Nonproliferation Treaty, which it signed nearly 50 years ago. That treaty forbids any non-nuclear-weapon states that are signatories from building atomic weapons, and requires them to allow in international inspectors. Iran has always contended that it has no interest in building atomic weapons, though documents that have emerged from the country — including a huge archive of documents spirited out of Iran in a raid by Israel last year — suggest that before 2003, Iran had an advanced program developing weapons designs.