KYIV, Ukraine — Russia launched one of its biggest aerial attacks this year at Ukraine, firing 574 drones and 40 missiles, the Ukrainian Air Force said Thursday. The attack mostly targeted western regions of the country, it said. The strikes killed at least one person and injured 15 others, according to officials.

Ukraine and its European allies have been buoyed by Trump's promise during a summit on Monday of security guarantees for Kyiv, but many questions remain unanswered. Officials told Reuters that the Pentagon is carrying out planning exercises on the support Washington could offer beyond providing weapons.