Tensions are escalating between Ukraine and Russia as the two countries have stepped up their airstrikes over the past two days, exchanging heavy fire.

Explosions are heard in Kiev and Kharkiv where, according to the mayor, buildings are burning. Officials say Ukraine received an overnight barrage of Russian drone strikes in retaliation for killing 21 of them and three children and wounding 110 others in Ukraine’s attack on the Russian city of Belgorod on Saturday.

The attack on the city of Belgorod followed Russia’s fierce offensive across Ukraine last Friday that killed 39 people and was described by Kiev as Russia’s biggest missile bombardment of the war so far.

Speaking to the BBC, the Ukrainian security source said more than 70 drones had been launched against Russian targets in “response to Russia’s terrorist attacks on Ukrainian cities and civilians”.

From the Russian attacks in Kharkiv, the well-known Kharkiv Palace hotel, where journalists-correspondents of foreign networks often stay, was hit by a missile, with the information speaking of at least four victims, without specifying their origin, if they were hotel employees, or foreign nationals. Among other things, an apartment complex was hit and eight people were injured, announced the governor of the Kharkiv region.

Ukraine’s air defense systems in the area around the capital Kiev were deployed late Saturday to repel a Russian drone attack, the region’s military command reported on Telegram.

“These are not military facilities, but cafes, residential buildings and offices,” Mayor Ihor Terekhov said on Telegram.

“On New Year’s Eve, the Russians want to bully our city, but we are not afraid – we are unbreakable and invincible,” he added.