Purely precautionary.That is how Israel is describing a nationwide security drill in which even its youngest citizens are being prepared for a worst case scenario. Civilians as well as soldiers are taking part in the country’s biggest home front defence exercise. Rocket fire, large-scale terrorist attacks, chemical strikes – all are being envisaged. Prime Minister Benjamin Netanyahu says it is not linked to any particular intelligence alert. But the drill is being watched closely in the region amid speculation about a possible Israeli attack on Iran’s nuclear facilities, which could provoke retaliatory missile strikes.