A Decimated Hezbollah Is a Serious Blow for Iran

The death of the Hezbollah leader Hassan Nasrallah in an airstrike has dramatically weakened a key Iranian deterrent against its archenemy, Israel.

Iran has long sought to have the proxies it supports in the region — including Hezbollah in Lebanon, Hamas in Gaza, and forces in Syria, Yemen and Iraq — serve as the front line in its long-running fight with Israel. But if its most important military asset, Hezbollah, has been decimated, it may have no choice but to respond, experts said Saturday.

The decisions it makes will have a significant impact on the next stage of a growing conflict that now threatens to engulf the region.

“Iran’s choices really range from ugly to unpalatable,” said Ali Vaez, the director of the Iran Project at the International Crisis Group, a conflict prevention organization.

Julien Barnes-Dacey, the Middle East and North Africa program director at the European Council on Foreign Relations, said Israel’s assassination of Mr. Nasrallah significantly raises the risk of a dangerous conflagration in the Middle East, and beyond.

“It really is a question of whether Hezbollah has the capacity to launch wide-ranging missile strikes on Israel at this point,” Mr. Barnes-Dacey said. If it does not, “this could now push Iran to make a dash for nuclear weapons because they see that as their only effective form of deterrence left standing.”