“There was kind of a desperation to carry out these attacks; they weren’t necessarily as well prepared,” a senior Israeli official said. “Even when they were thwarted there was a sense they’d done something. They need to show some results.”

Analysts say that the increased planning was also evidence of deepening anger in Tehran as international sanctions took hold. Simple revenge is a possible motive, they say.

Hezbollah has sworn to retaliate against Israel for the 2008 assassination of Imad Mughniyah, the group’s former security chief, who was killed in a car bombing in Syria. Iran blames Israel for killing at least four Iranian nuclear scientists, several with magnetic bombs placed on their vehicles. Efraim Halevy, formerly head of the Mossad, conceded that the shadow war was not just one-sided with “a measure of attack on both sides.” He drew a distinction between “innocent bystanders” and “people who are threatening you.”

The Israelis count an assassination attempt against the Israeli consul general in Istanbul and the killing of a Saudi diplomat in Karachi, both in May 2011, as the beginning of the recent offensive. The United States said it had thwarted an Iranian-backed plot last year to kill the Saudi ambassador in Washington with the help of a Mexican drug gang.

But the intensity of the new offensive came into focus in February when tactics similar to those used in the killings of Iranian scientists were deployed against Israelis. A motorcyclist pulled up alongside a vehicle belonging to the Israeli Embassy in New Delhi and attached a small explosive device. The wife of an Israeli defense official was wounded in the ensuing blast, as were three others, but all survived.

In the Georgian capital, Tbilisi, on the same day, a driver for the Israeli Embassy “found something stuck to the car with a magnet,” he told the Georgian television station Real TV. Investigators cordoned off the area while explosives experts defused the bomb. No one was harmed.

The following day, an explosion rocked a rented home in Bangkok. One man lost his legs after a bomb exploded as the Bangkok police tried to arrest him. A second man was arrested by the police at Bangkok’s Suvarnabhumi Airport trying to flee the country. A third suspect sought in the case was apprehended in neighboring Malaysia, where he is still fighting extradition.