Senior Ukrainian officials led 60 foreign diplomats on a tour of damaged government offices in the heart of Kiev on Monday, a day after Russia’s largest aerial attack on Ukraine since the war began more than three years ago.

Russia’s strikes on Sunday involved more than 800 drones and decoys. Four people were killed as drones hit apartment buildings, and a plume of smoke rose from the capital’s main government building where top officials have their offices.

It's believed to be the first time a Russian attack has struck the 10-storey, Soviet-style building, which was built almost a century ago and has an imposing half-circle facade.

During the tour given to the diplomats, Ukrainian Prime Minister Yuliia Svyrydenko, Foreign Minister Andrii Sybiha and Interior Minister Ihor Klymenko showed them burnt-out offices littered with charred debris.

'Hard to resolve'

A deadline by US President Donald Trump, set in August, for the Kremlin to change course or face severe consequences has passed.

Trump has blamed both sides in the war for the ongoing fighting.

Trump said on Sunday that he expected to speak with Russian President Vladimir Putin in the next couple of days and acknowledged that the conflict had proved harder to resolve than he anticipated.

Ukraine and European leaders are urging Washington to step up economic sanctions on Russia.

EU officials travel to the US

A team of European officials, led by European Union sanctions envoy David O’Sullivan, will visit the US Treasury to discuss various forms of economic pressure to exert on Russia, including new sanctions, a person familiar with the meeting told The Associated Press.

Ukrainian officials and analysts have previously warned that Russia intends to escalate its barrages to include more than 1,000 drones per day before the end of the year.