Parties to Iran's 2015 nuclear deal met in Vienna on Sunday for emergency talks called in response to an escalation in tensions between Iran and the West that included confrontations at sea and Tehran's breaches of the accord.
Britain, France, Germany, Russia, China and Iran have been trying to salvage the pact since the United States withdrew from it in May 2018 and re-imposed and toughened sanctions on Iran, crippling an already weak economy.
The European-led efforts to protect trade with Iran against the US sanctions have yielded nothing concrete so far. Earlier this month, Tehran followed through on its threat to increase its nuclear activities in breach of the agreement.
"All our steps taken so far are reversible if other parties to the deal fulfill their commitments," an Iranian diplomat told Reuters before the extraordinary meeting was due to start.
In response to the sanctions, Iran said in May it would decrease its commitments under the nuclear pact. Under the deal, most international sanctions against Tehran were lifted in return for limitations on its nuclear work.
So far, Iran has breached the limit of its enriched uranium stockpile as well as enriching uranium beyond a 3.67 percent purity limit set by its deal with major powers, defying a warning by Europeans to stick to the deal despite US sanctions.
The UN nuclear watchdog, policing the deal, has confirmed the measures announced by Tehran.
"[Trade vehicle] INSTEX , along with other measures, will be discussed in the meeting. Other parties should accelerate their efforts, otherwise Iran will take a third step," the diplomat said.
The meeting in Vienna comes after Iran’s elite Revolutionary Guards seized a British-flagged oil tanker on July 19, two weeks after British forces captured an Iranian oil tanker near Gibraltar which it said was violating sanctions on Syria.
Iran's senior nuclear negotiator Abbas Araqchi said on Sunday Britain's seizure of the Iranian oil tanker was a violation of the nuclear pact.
"We witnessed the seizure of an oil tanker carrying Iranian oil in the Strait of Gibraltar which in our view is a violation of [the nuclear deal]," Araqchi said.
"And the countries who are part of [the nuclear deal] shouldn't create obstacles for the export of Iranian oil."
Britain has called for a European-led naval mission to ensure safe shipping through the Strait of Hormuz, a vital international oil shipping route. An Iranian government spokesman said on Sunday such a mission would send a "hostile message".
Britain said on Sunday Royal Navy destroyer HMS Duncan had arrived in the Gulf to join a British frigate escorting British-flagged ships through the Strait.
Iran has threatened to disrupt oil shipments through the waterway, where several oil tankers have been attacked, if the United States tries to strangle its economy with sanctions on its vital oil exports.