Israel has called on Europe to impose sanctions on Iran after Tehran surpassed its limit of enriched uranium.

Israeli Prime Minister Benjamin Netanyahu today told European states to sanction the Islamic republic after it said it breached an agreed ceiling on its uranium reserves.

'You committed yourselves to act as soon as Iran violated the nuclear agreement,' a statement from his office quoted him as saying. 'So I say to you: Do it. Just do it.'

Iran's enriched uranium stockpile passed the 300kg limit prescribed by the 2015 nuclear deal with world powers, according to media reports.

The semi-official Fars agency attributed its Monday report to an unnamed source, who said UN inspectors had recently weighed Iran's stockpile of low-enriched uranium.

Iranian President Hassan Rouhani (centre) and the head of Iran nuclear technology organisation Ali Akbar Salehi inspecting nuclear technology in April this year

Iran has vowed to begin enriching its stockpile of uranium to higher levels later this month if world powers fail to negotiate new terms for the nuclear accord following the US decision to withdraw from the agreement and restore crippling sanctions.

European countries have repeatedly urged Iran to abide by the deal.

The unravelling of the landmark nuclear agreement comes amid heightened tensions in the Persian Gulf, where Iranian forces shot down a US drone last month.

European countries that are still a part of the nuclear accord face a July 7 deadline imposed by Tehran to offer a better deal and long-promised relief from U.S. sanctions, or Iran will also begin enriching its uranium closer to weapons-grade levels.

Breaking the stockpile limit by itself doesn't radically change the one year experts say Iran would need to have enough material for a bomb.

An Iranian security official in protective clothing walks through part of the Uranium Conversion Facility just outside the Iranian city of Isfahan

Coupled with increasing enrichment, however, it begins to close that window and hamper any diplomatic efforts at saving the accord.

The United States withdrew from the nuclear deal last year and reimposed biting sanctions on Iran's crucial oil exports and financial transactions as well as other sectors.

Tehran, which has sought to pressure the remaining parties to save the deal, on May 8 announced it would no longer respect the limit set on its enriched uranium and heavy water stockpiles.

'Israel will not allow Iran to develop a nuclear weapon,' Netanyahu said today.

'I am also calling on all European countries. Honour your commitment,' he added. 'You committed to activate the automatic sanctions mechanism set by the (UN) Security Council.'

Netanyahu has long campaigned against the 2015 agreement. Iran insists its nuclear programme is entirely for civilian purposes.

Israel is considered the leading military power in the Middle East and is widely believed to possess its sole, if undeclared, nuclear arsenal.

'I worry about the snowball effect,' said Corey Hinderstein, a vice president at the Washington-based Nuclear Threat Initiative who once led the US Energy Department's Iran task force.

'Iran now takes a step which puts Europe and the other members of the deal in an even-tougher position.'

Under terms of the nuclear deal, Iran agreed to have less than 300 kilograms (661 pounds) of uranium enriched to a maximum of 3.67%.

Previously, Iran enriched as high as 20%, which is a short technical step away from reaching weapons-grade levels.

It also held up to 10,000 kilograms (22,046 pounds) of the higher-enriched uranium.

Experts described the enrichment and stockpile limits in the deal as a sort of sliding scale.