BERLIN — A magnetic bomb detonated on a diplomatic car in New Delhi. The police uncovered a cache of explosives at a golf course in the Kenyan city of Mombasa. Five Israeli tourists and a Bulgarian bus driver were killed in an attack outside the airport in the Black Sea coastal city of Burgas.


These were just a few of what some Israeli and American intelligence officials say were nearly a dozen plots that form the backbone of a continuing offensive by Iran and Hezbollah against Israel and its allies abroad. But the links seem tenuous at times, the tactics variable, the targets scattered across the globe, from the Caucasus to Southeast Asia to the Mediterranean.


“This is not a spy thriller that necessarily has a plot readers can follow from page to page,” said Matthew Levitt, director of the program on counterterrorism and intelligence at the Washington Institute for Near East Policy. “Iran and Hezbollah both thrive on reasonable deniability.”


Analysts say the shadow war pitting Israel against Iran and Hezbollah has more in common with the cloak-and-dagger maneuverings of the C.I.A. and the K.G.B. during the cold war than the publicity-hungry terrorism campaign of Al Qaeda. It represents a return to the idea that the most effective attack is often an ambiguous one.


“They want just enough ambiguity that you can’t nail down that they did it, the seed of doubt that makes it difficult for Israel or the United States to respond,” said Andrew Exum, a senior fellow with the Center for a New American Security in Washington. The undercover conflict signaled “a return to the black arts of the cold war,” he said.


After the blast in Bulgaria, both Iran and Hezbollah denied involvement almost as quickly as Prime Minister Benjamin Netanyahu of Israel pointed the finger at them. American and Bulgarian officials backed the assessment off the record, but would not say so openly. There has been little hard evidence presented to show how or by whom the plots were coordinated.


Israeli intelligence has evidence of many telephone calls between Lebanon and Burgas in the two months before the bombing, according to a senior government official who spoke on the condition of anonymity because the information is classified, with the volume intensifying in the three days leading up to it.


But they are no more prepared to expose the details of their counterintelligence work publicly than the attackers are to claim responsibility. “We know the sources in Lebanon,” though not the identity of those on the other end in Bulgaria, the official said. “They shouldn’t know that we know the numbers in Lebanon.”


Weeks after the attack, the Bulgarian investigation has largely stalled. Officials there have yet to identify the attacker, also killed in the blast, or his suspected accomplices. They are hesitant to declare Hezbollah responsible without ironclad proof, given that the European Union has never designated the group a terrorist organization.


European allies expect more concrete evidence than the volume of calls before taking steps against Hezbollah. They maintain “some skepticism that it was Hezbollah as an organization itself, and not, for instance, Iran using individuals with some Hezbollah affiliation,” said a senior security official in Germany.


The investigation in New Delhi appears further along, but there, too, diplomatic and trading ties leave India with a dilemma. Iran is a major supplier of oil to India, which has struggled to balance relations with Iran, Israel and the United States.


The Indian police issued warrants in March for three Iranian citizens in connection with the New Delhi attack. But when The Times of India recently reported that the police had identified Iran’s Revolutionary Guards as responsible, officials immediately denied the report.


Several of the plots have been hasty and even sloppy. In Thailand, the suspects set off an explosion in their own safe house. Many other suspected plots failed or were disrupted before they materialized. That gave some experts the impression that the assaults were planned in a hurry, perhaps because Iran and Hezbollah scrambled to lash out after a string of covert attacks on Iran’s nuclear program. The civil war in Syria, which threatens the government of a key Iranian ally, may be another spur to action.


“We see Iran and Hezbollah as monoliths without realizing there is internal competition, dissent, factionalism, and these things become important when we have external pressures like we do now,” said Rashmi Singh, a lecturer at the Center for the Study of Terrorism and Political Violence at the University of St. Andrews in Scotland. “What’s happening in Syria is making this more acute than ever,” she said.


The proliferation of plots has kept Israel on guard. It was less cat-and-mouse than Whac-A-Mole, with plots popping up in Africa, Europe, South Asia and Southeast Asia.