At the core of the Israel-Iran dispute is the latter's nuclear program. But it's been playing out in a strange way, in a shadow war that stretches across continents.
Almost immediately after a bomb killed several Israeli tourists and wounded more than 30 on a Bulgarian bus Wednesday, Israel blamed Iran and its Lebanese ally Hezbollah.
"All signs point to Iran," said Israeli Prime Minister Benjamin Netanyahu. He also accused Iran and Hezbollah of being behind other recent attempted or actual attacks on Israeli targets in India, Thailand, Cyprus and elsewhere.
On the other side of this conflict, Iran blames Israel for the killings of five Iranian nuclear scientists in the past few years. In addition, the Stuxnet computer virus in 2010 destroyed a large number of centrifuges that are a vital part of Iran's nuclear enrichment process. No one has claimed responsibility, though the U.S. and Israel are widely believed to be behind that effort.
Israel has not yet provided evidence of an Iranian role in Wednesday's bombing, and the Bulgarian investigation is still under way. Authorities are trying to identify a man with a fake Michigan driver's license who is suspected of being the suicide bomber.
Nonetheless, Netanyahu did not hesitate to make a direct link between the attack and Iran's nuclear program.
"The most dangerous country in the world cannot have the most dangerous weapons on Earth," the prime minister said.
Iran and Israel have been wary adversaries ever since Iran's Islamic Revolution in 1979. But the standoff over Iran's nuclear program has escalated tensions over the past few years.
"The shadow war has increased in intensity," says Dan Bynam, a professor at Georgetown University's School of Foreign Service and the author of A High Price: The Triumphs and Failures of Israeli Counterterrorism. "We've certainly seen a lot of back-and-forth recently."
Israel believes Iran is determined to acquire nuclear weapons capability, and has warned repeatedly that it's prepared to take military action if Iran's program is not halted. Iran, meanwhile, insists its nuclear program is for peaceful, civilian purposes. The international efforts to negotiate a solution have been stalled.
The latest violence further complicates the nuclear question, says Bynum, but both sides have motivations.
"The actions attributed to Israel can help reassure the Israeli people that the government is doing something to set back the Iranian program," he says. "Limited action may ease the political pressure to take more massive action."
The Iranian logic, he says, may be similar. "Iran is already being hit, and this may be a way for Iran to show it's responding," he says.
Still, the concern is that these attacks could provoke a much larger confrontation between the two countries.
"There's certainly the risk that this shadow war comes out of the shadows and becomes a much hotter conflict," says Robert Satloff, head of the Washington Institute for Near East Policy. "At a certain point, a government needs to respond in public and overt ways to the murder of its citizens."
Satloff stresses that Iranian attacks against Israel have a long history. Wednesday was the anniversary of a 1994 bombing at a Jewish cultural center in Argentina that killed 85 people. An Argentine investigation found that Iran was responsible.
"This has been part and parcel of Iran's strategy for many, many years," Satloff says. Still, he acknowledges that the tempo is picking up.
"The ticking clock on Iran's nuclear program and the rising expectation that Israel may choose to act independently are all things that feed this process," he says.