Arch-foes Israel and Iran have long fought an undeclared shadow war across the Middle East, landing blows in Lebanon, Syria and inside the Islamic republic itself.
More recently, the battle has moved to the high seas, with a series of mysterious attacks and sabotage incidents mainly in the Red and Arabian Seas.
Analysts now fear the tit-for-tat attacks could escalate, warning that the protagonists are "playing with fire".
Israel has vowed to stop Iran, whose leaders have threatened to "wipe it off the map", from acquiring a nuclear bomb -- a goal Tehran denies pursuing.
The Islamic republic meanwhile has provided arms, training and money to allied militias in a regional "axis of resistance" against the Jewish state and its ally the United States.
In the latest attack Iran blamed on Israel, a blast hit Iran's enrichment facility in Natanz Sunday, complicating diplomatic efforts to salvage a tattered 2015 deal on Tehran's nuclear programme.
Then on Tuesday, Israeli-operated ship the Hyperion Ray was attacked near the Emirati port of Fujairah, the latest in a string of off-shore attacks.
- Spy missions, assassinations -
Israel has often fought Tehran's allies, including Lebanon's Hezbollah, Hamas in the Palestinian enclave of Gaza, and pro-Iran fighters in Syria.
The Jewish state has also launched cyberattacks and spy missions, such as a 2018 Mossad operation that netted a treasure trove of Iranian nuclear documents from a Tehran warehouse.
Israel's Prime Minister Benjamin Netanyahu in recent years relished having a White House ally in Donald Trump, who waged a hardline "maximum pressure" campaign against Iran.
Trump in 2018 ripped up the 2015 agreement that had granted Iran sanctions relief in return for limits on its nuclear activities, a deal Israel always rejected as inadequate.
Under Trump, the US also killed revered Iranian General Qasem Soleimani in a Baghdad drone strike early last year, a move that brought Tehran and Washington to the brink of war.
Israel was then blamed for the assassination in Tehran last November of Iran's top nuclear physicist Mohsen Fakhrizadeh, the latest Iranian atomic scientist to meet a violent death.
But the dynamic has shifted since US President Joe Biden took power and started efforts to revive the nuclear deal, while taking a cooler stance towards Netanyahu.
- 'Maritime war' -
Sima Shine of Israel's Institute for National Security Studies said it was debatable when the shadow war started.
But she described a chain of events relating "to the nuclear sphere and ... the attempt of Iran to establish itself in Syria, and the attempt of Israel to stop it."
"In the last couple of weeks we also saw the maritime war come out publicly, after it was secret for two years, between Iran and Israel," she said.
Iran first hinted at attacks on its tankers in the Red Sea in 2019, as Israel sought to curb its alleged arms transfers and oil shipments to allies.
Then February 25, an Israeli cargo ship, the MV Helios Ray, was hit at sea. Attacks have since multiplied, often involving mines attached above the water line, where they disable rather than sink ships.
The Iranian ship Shahr-e-Kord was hit near Syria, followed by the Israeli container ship Lori in the Arabian Sea, and the Iranian cargo ship Saviz in the Red Sea.
- 'Grey-zone level' -
"Thus far, the maritime conflict between Iran and Israel has remained at a low-intensity, grey-zone level, below the threshold of declared hostilities," wrote researcher Farzin Nadimi of the Washington Institute for Near East Policy.
He said it appeared both sides are "seeking to avoid escalation that might disrupt their respective shipping lanes and economies".
But, he added, "both countries have substantial special naval warfare capabilities and experience, so neither is likely to settle for anything less than maritime superiority."
Nadimi warned that the pace of attacks could "accelerate further, while also expanding to a larger geographical area" and using new means such as submarines, longer-range drones and fast-attack vessels.
While "both sides have sought to keep their tit-for-tat maritime attacks under control," he said, "they pose a substantial risk of miscalculation and escalation that could jeopardise international shipping."
Menahem Merhavy, an Iran specialist at the Hebrew University of Jerusalem, agreed that neither side wants escalation.
But, he warned, "things can get out of hand. Both Israelis and Iranians are aware of the possibility of that and they are trying to avoid it."
He said Iran's hand is weakened by sanctions and the Covid pandemic, but also by the desire to "come as clean as possible to the table" of new diplomatic efforts over its nuclear activities.
"On Israeli side," he said, "the greatest risk is actually its relation with the US."
With a shadow war on the high seas and operations such as the alleged Natanz attack, he said, "we are playing with fire here."