TEHERAN • The raid alone was brazen enough. A team of Israeli commandos with high-powered torches blasted their way into the vault of a heavily guarded warehouse deep in Iran and made off before dawn with 5,000 pages of top-secret papers on the country's nuclear programme.

Then in a TV broadcast a few weeks later, in April 2018, Israeli Prime Minister Benjamin Netanyahu cited the contents of the pilfered documents and coyly hinted at equally bold operations still to come. "Remember that name," he said, singling out scientist Mohsen Fakhrizadeh as the captain of Iran's covert attempts to assemble a nuclear weapon.

Now Dr Fakhrizadeh has become the latest casualty in a campaign of audacious covert attacks seemingly designed to torment Iranian leaders with reminders of their weakness.

The operations are confronting Iran with an agonising choice between embracing the demands of hardliners for swift retaliation, or attempting to make a fresh start with the less implacably hostile administration of United States President-elect Joe Biden.

Dr Fakhrizadeh's killing was the latest in a decade-long pattern of mysterious poisonings, car bombings, shootings, thefts and sabotage that has afflicted the Islamic Republic. Most have hit largely anonymous scientists or secretive facilities said to be linked to its nuclear programme, and almost all have been attributed by US and Iranian officials to Iran's great nemesis, Israel, whose officials - without formally acknowledging responsibility - have all but openly gloated over the repeated success of their spies.

Seldom has any country demonstrated a similar ability to strike with apparent impunity inside the territory of its fiercest enemy, said Brookings Institution researcher Bruce Riedel, a former Central Intelligence Agency official with experience in Israel. "It's unprecedented," he said. "And it shows no sign of being effectively countered by the Iranians."

With the killing of their top nuclear scientist, the assassination of General Qasem Soleimani by a US drone strike in January and an Israeli hit team's fatal shooting of a senior Al-Qaeda leader in Teheran in August, Iranians are now grappling with a new sense of vulnerability and demands to purge suspected collaborators. Most of all, they are debating how to respond at a delicate moment.

Iran has endured years of devastating economic sanctions under a campaign of "maximum pressure" from President Donald Trump, and many Iranian leaders are desperately hoping for some measure of relief.

Mr Biden has pledged to seek to revive a lapsed agreement that lifted sanctions in exchange for a halt to nuclear research that might produce a weapon.

NYTIMES