Ukrainian President Volodymyr Zelenskyy warned airlines, insurers and passengers Tuesday that Russian airspace would remain "completely unsafe” and filled with Ukrainian drones for as long as the war continues.

"Today, we want to warn every airline that uses Russian airspace, every insurer, and everyone who still uses Russia's key airports: Russian airspace is becoming completely unsafe," he said on X. "There will simply be drones in Russia's skies on a scale that has to be taken into account," he added, warning "the safe days in Russia's skies are over."

Zelenskyy also criticized representatives of Ukraine's international partner nations for taking summer holidays while his country is fighting for its survival.

"For the past two weeks, Europe and the whole world - which is helping us - have been on holiday," he lamented to journalists on Tuesday.

He said Russia had used the time to launch attacks on Ukrainian infrastructure, partly to disrupt the start of the school year, which was marked nationwide on Tuesday.

Zelenskyy accused Western partners of practising "diplomacy by the book." Their approach, he said, was: "If it's holiday time, then it's holiday time."

For him, however, this was a "very unpleasant reality." He had repeatedly appealed to the international community for help in recent weeks.

Zelenskyy did not specify who he was referring to. Just under a week ago, European Council President António Costa, British Prime Minister Andy Burnham and other leaders travelled to Kyiv for Ukraine's Independence Day.

German Chancellor Friedrich Merz and French President Emmanuel Macron took part in the discussions via video link, pledging further aid.

The Ukrainian capital in particular has been under intensified Russian bombardment with drones and ballistic missiles for several weeks.

Kyiv has repeatedly urged its Western partner states to increase supplies of ammunition for air defence systems, which are in short supply.