The U.S. and Iran exchanged air attacks over the weekend amid their fragile ceasefire in the countries’ months-long war. 

The United States said it struck Iran’s air-defense radar and drone sites, which was followed by U.S. ally Kuwait coming under attack after Iran said it was retaliating, according to The Wall Street Journal. 

Diplomatic efforts to end the war, in which Israeli joined the U.S. against Iran, have stalled over Iran’s pursuit of a nuclear weapon. The allied countries initially began launching air strikes on Iran on Feb. 28, after failed negotiations to get Iran to wind down its nuclear -enrichment program.

The U.S. attack this past weekend was prompted by Iran shooting down an American MQ-1 drone, Central Command said. 

U.S. fighters also shot down two Iranian attack drones that posed a threat to ships, The Journal also reports.