A deadly drone strike on an Israeli-operated tanker that’s been blamed on Iran has raised the stakes in a years-long shadow war between Israel and Iran. The two countries have attacked each other on land, by air and at sea in recent years, in Iran’s case sometimes through allies in the region. The July 29 attack on the tanker in the Gulf of Oman, for which Iran denied involvement, led to threats of retaliation from Israel. It also prompted warnings of potential reprisals from the U.K., which lost a crew member, and the U.S., which created a maritime force with partners in 2019 to help protect sea lanes in the Middle East.

1. Why are Iran and Israel enemies?

They were allies starting in the 1950s during the reign of Iran’s last monarch, Shah Mohammad Reza Pahlavi, but the friendship abruptly ended with the Iranian Revolution in 1979. The Islamic Republic of Iran adopted a strong anti-Israel stance, decrying the Jewish state as an imperialist power in the Middle East. Iran has supported groups that regularly fight Israel, notably Hezbollah in Lebanon and the Palestinian group Hamas. Israel regards Iran’s potential to build nuclear weapons as a threat to its existence and is thought to be behind a campaign of sabotage against the country’s atomic program.

2. Where has the shadow war been taking place?

• At sea: Tit-for-tat attacks on commercial vessels began in 2019. Neither Israel nor Iran has accepted responsibility for the hits, though they are widely thought to be to behind them. Previous targets have included Iranian tankers carrying oil destined for Syria; an Iranian ship off the coast of Yemen that served as a floating base for the Islamic Revolutionary Guard Corps, the country’s premier military force; and cargo ships belonging to or linked to Israelis, including a car carrier attacked in February.

• In Iran: Israel is widely thought to be behind the assassination of five Iranian nuclear scientists since 2010 and several attacks on nuclear sites inside the country. Iran accused Israel and the U.S. of being behind the killing of scientist Mohsen Fakhrizadeh in an ambush on the outskirts of Tehran in November last year. Both Israel and the U.S. declined to comment on the killing. In another incident in April this year, Iran blamed Israel and vowed revenge for an explosion at its largest uranium enrichment facility in Natanz, which it said caused significant damage to its centrifuges. It was the second time in less than a year that the site had been hit by a suspicious blast. Israel neither confirmed nor denied it was responsible for either attack.

• In Syria: Since civil war erupted a decade ago in Syria, which borders Israel, Iran has expanded its military presence in the country to support its ally, President Bashar al-Assad. In response, Israel has been conducting an increasingly open campaign in Syria against targets linked to Iran, resulting, according to media accounts, in the deaths of some Iranians. Israeli jets have repeatedly struck military sites around the capital, Damascus, and beyond.

• In Lebanon: This is the oldest front in the battle and is fought indirectly. Shiite Muslims in Lebanon formed what would become Hezbollah in 1982 in reaction to Israel’s occupation of the country’s south. Their movement was inspired by the revolution in Shiite-majority Iran, and Hezbollah to some extent became a proxy force for Iran’s Revolutionary Guards. Since the last war between Israel and Lebanon in 2006, the military wing of Hezbollah has built a vast arsenal of rockets along Israel’s northern border, according to the Israeli military. Israel, according to media reports, has targeted key components of Hezbollah’s missile program in Lebanon, while Hezbollah has on occasion retaliated by firing rockets into Israel and attacking Israeli forces along the border.

3. What are the goals of the two sides?

For the most part, both seek to avoid conspicuous, direct clashes, which would risk escalation to all-out war, preferring instead to act with plausible deniability. Israel’s objectives include thwarting Iran’s nuclear program and containing its wider influence in the region. Recent shadow attacks by Iran are widely seen as brinkmanship aimed at improving its leverage in talks to revive the 2015 accord in which world powers lifted sanctions in exchange for restrictions on Tehran’s nuclear program. Israel has been a vocal critic of the agreement. The U.S., under President Donald Trump, pulled out of the deal in 2018 and reimposed sanctions, prompting Iran eventually to begin violating the nuclear limits it had agreed to.

4. What are the risks?

The risks of escalation are significant for both countries. According to Israel’s military, Hezbollah has an arsenal of around 130,000 missiles, which could cause substantial damage if unleashed on Israel. A step-up of the conflict could inflame the region and likely would further weaken Iran’s economy, already beleaguered by years of sanctions and a devastating Covid-19 outbreak.

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