Iran in the past has accused Israel of causing a series of spectacular and sometimes bloody mishaps to its nuclear programme. Israeli officials do not comment on any involvement in those events, although some have publicly expressed satisfaction at the setbacks.
Feeling the heat from unprecedented new sanctions, Iran's clerical establishment has brandished its sword by threatening to block the main Mid-East oil shipping route, starting to enrich uranium at an underground bunker and sentencing an Iranian-American citizen to death on spying charges.
State TV said a "letter of condemnation" had also been sent to Britain, saying the killing of Iranian nuclear scientists began after the head of Britain's MI6 spy service announced intelligence operations against states seeking nuclear weapons.
The West says Iran's nuclear programme is aimed at building a bomb. Tehran says it has the right to peaceful nuclear power.
Tehran has urged the U.N. Security Council and Secretary-General Ban Ki-moon to condemn the latest killing.
The combined measures mean Iran may fail to sell all of the 2.6 million barrels a day of exports it relies on to feed its 74 million people. Even if it finds buyers, it will have to offer steep discounts, cutting into its desperately-needed revenue.
On Tuesday shipping sources told Reuters Iran was storing an increasing supply of oil at sea - as much as 8 million barrels - and was likely to store more as it struggles to sell it.
Iran denies it is having trouble: "There has been no disruption in Iran's crude exports through the Persian Gulf ... We have not stored oil in the Gulf because of sanctions as some foreign media reported," oil official Pirouz Mousavi told the semi-official Mehr news agency on Friday.
The sanctions are causing real hardship on the streets, where prices for basic imported goods are soaring, the rial currency has plummeted and Iranians have been flocking to sell rials to buy dollars to protect their savings.
The pain comes less than two months before a parliamentary election, Iran's first since a presidential vote in 2009 that was followed by eight months of street demonstrations.
Iran's authorities successfully put down that revolt by force, but since then the "Arab Spring" has shown the vulnerability of authoritarian governments in the region to protests fueled by anger over economic difficulty.
Iran has threatened to block the Strait of Hormuz leading to the Gulf if sanctions are imposed on its oil exports, and has threatened to take unspecified action if Washington sails an aircraft carrier through the strait, an international waterway.
Military experts say Tehran can do little to fight the massive U.S.-led fleet that guards the strait, but the threats raise the chance of a miscalculation that could lead to a military clash and a global oil crisis.
The Pentagon said on Friday that small Iranian boats had approached close to U.S. vessels in the strait last week, although it said it did not believe there was "hostile intent."
The United States and Israel have not ruled out military action if diplomacy fails to resolve the nuclear dispute. Iran says it would retaliate if attacked.
The tension has caused spikes in global oil prices in recent weeks, although prices eased at the close of last week's trading on the prospect of reduced demand in economically stricken European countries. Brent crude fell 82 cents to settle at $110.44 a barrel on Friday.
The chances for an imminent easing of tension look even more remote as the nuclear deadlock continues because of Iran's refusal to halt the sensitive nuclear work.
Last week Iran began enriching uranium underground - the most controversial part of its nuclear programme - at a bunker deep below a mountain near the Shi'ite holy city of Qom.
Nuclear talks with major powers collapsed a year ago. Iran says it wants the talks to resume, but the West says there is no point unless it is willing to discuss a halt to uranium enrichment, which can be used to make material for a bomb.
(Additional reporting by Mitra Amiri; Writing by Parisa Hafezi; Editing by Peter Graff)