The United States has attacked three sites in Iran, inserting itself into Israel’s war aimed at destroying the country’s nuclear program in a risky gambit to weaken a longtime foe that prompted fears of a wider regional conflict.

European nations worked Monday to keep alive diplomatic efforts to curb the Israel-Iran war as the two countries traded strikes following the United States’ weekend attack on Iran’s nuclear program.

The all-caps post came hours after weekend bombings in Iran rattled oil markets and reignited fears of rising fuel costs.