Russia and Ukraine traded their heaviest strikes in months, fueling fears of escalation and further strain on oil supplies.

Ukraine fired more than 400 drones toward Moscow in its latest major attack on the Russian capital, the city’s mayor said Monday. The blitz came hours after Russia bombarded Kyiv and other Ukrainian cities with ballistic missiles in a relentless cycle of tit-for-tat strikes that make a settlement to end Moscow’s more than 4-year-old all-out invasion appear a distant possibility.