Israel has vowed its Iran retaliation will be swift and ‘painful’ — but what might that look like?

Such a strike would “mark a new high in the tit-for-tat pattern of escalation, and will likely unfurl a chain reaction of unforeseeable events that will endanger U.S. and Western assets, interests and personnel in the region,” Burcu Ozcelik, a senior research fellow at the Royal United Services Institute think tank in London, told NBC News.