On Tuesday, millions of Israelis were headed into bomb shelters and blastproof rooms.

The country was holding it's largest-ever civil defense drill.

The drill is part of a five-day exercise aimed at testing the country's readiness for an enemy military strike.

Israel is sounding it's air raid sirens and simulating rocket attacks on its biggest cities. The drill comes at a time of rising concerns over Iran's recent nuclear activity.

Israeli officials, however, say this drill is not a direct response to worries over Iran.