'This is a country that hates war,' says gov't spokesman David Mencer
Both Iran and Hezbollah are expected to retaliate for the killings
Killings of Haniyeh and Shukr could increase threats to Israel and US forces
Haniyeh was in Iran for inauguration of newly elected President Pezeshkian
Israel killed Hezbollah's 'most senior military commander' in its stronghold in Beirut