Ukraine reported early Friday that Russian drones and missiles targeted its territory, causing multiple explosions and fires. Officials said debris from intercepted projectiles injured four people, two of whom were hospitalized, BBC reported.

Air raid alerts have been lifted in some parts of Ukraine, but they are still in effect in places like Kharkiv, Sumy, and Luhansk.

Earlier this week, US President Donald Trump stated that Russian President Vladimir Putin vowed a strong response to Ukraine’s recent drone attacks on Russian airbases.