After years of high-level US pressure on its ally to show restraint, Israel's purported attack on Iran takes the region and Western-led diplomacy into uncharted territory.
Iran and Israel have long waged a shadow war, marked by assassinations of Tehran's nuclear scientists and attacks on Israel by the clerical state's allies in the Arab world such as Lebanon's Hezbollah, but the United States has put a top priority on preventing a wide-scale war.
The deadliest-ever assault on Israel, carried out on Oct. 7 by Iranian-backed Palestinian militants Hamas, shook Israel and solidified its resolve, with President Joe Biden's administration resigned to limiting rather than preventing a regional flare-up.
Direct Iranian and Israeli attacks are "a milestone, because it's completely changed the rules of engagement between the two adversaries," said Merissa Khurma, director of the Middle East program at the Wilson Center.
"It has also elevated tensions across the region. It has made the spectre of all-out war very real for many countries in the region," she said.
Israel early Friday appeared to have struck near the Iranian city of Isfahan, after Iran last weekend carried out its first-ever direct assault on Israel with a barrage of 300 missiles, drones and rockets.
