He said: "If Europeans hesitate in responding to out demands, Iran is entitled to resume its nuclear activities".
The ayatollah made five demands, calling on them to "guarantee the total sales of Iran's oil", meaning Europe must promise to make up for any oil sales from third countries which are cancelled because of U.S. sanctions.
He said European banks "must guarantee business transactions with the Islamic Republic".
In the wake of Washington's exit from the deal, European parties to the nuclear pact are working to find a way to keep it in effect.
@hrome2: "Currently, we are not starting enrichment of 20% but we must be ready so that if it becomes necessary, and we see the JCPOA become useless, the activities that were stopped because of the JCPOA can be resumed".
Highlighting how hard it will be, the U.S. Treasury announced Thursday more sanctions on several Iranian and Turkish companies and a number of aircraft in a move targeting four Iranian airlines.
New U.S. sanctions are being phased in, but already many non-U.S. companies have said that they will also likely have curtail operations in Iran for fear of losing access to the much more important American market.
He also said he would reinstate U.S. nuclear sanctions on Iran and impose "the highest level" of economic bans on the Islamic Republic.More news: Deadly drug in teething products forces FDA action
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"European banks should safeguard trade with the Islamic republic".
The supreme leader called on nations to "guarantee the total sales of Iran's oil", which means the continent will have to make up for any oil sales which have been cancelled because of U.S. sanctions.
A senior diplomat at IAEA headquarters said this was not prompted by any lack of co-operation or change of behaviour on Iran's part. Some Western companies have already quit Iran or said they may have to leave because of the new United States sanctions.
He said talks would continue over the next few weeks "particularly at an expert level", after which Iran would decide whether or not to stay in the accord.
Speaking before the meeting, a senior Iranian official rejected any attempt to link the deal, known as Joint Comprehensive Plan of Action (JCPOA) to other such issues, saying it would mean "we lose JCPOA and we (would) make the other issues even more complicated to resolve", adding that it was pointless for the Europeans to try to "appease" Trump.
Trump denounced the accord, completed under his predecessor, Barack Obama, because it did not cover Iran's ballistic missile program, its role in Middle East conflicts or what happens after the deal begins to expire in 2025.
The official said that if they were unhappy with how things panned out they would seek a ministerial meeting and then decide.
The International Atomic Energy Agency, which polices the pact, said Thursday that Iran continued to comply with its terms, but could be faster in allowing snap inspections.
Khamenei said Iran reserves the right to expand its nuclear program beyond the limits of the accord unless European banks facilitate trade and Europeans provide assurances that they will buy Iranian oil if the USA attempts to disrupt crude sales.