Kneeling down with a can of white spray paint in his hand the mayor of the Lithuanian capitol Vilnius sprayed "Putin, the Hague is waiting for you" on a road opposite the Russian embassy in the city this week.

"Our city is always supportive of art, especially art which sends a message of peace," said Remigijus Simasius, 48, as he sprayed the giant letters of the 20-meter long slogan, using a long-lasting paint.

"The message of peace is that war criminals must end up in Hague, in the criminal court", he added.

In Lithuania, once ruled from Moscow but now part of NATO and the European Union, people have watched Russia's invasion of Ukraine with horror and outrage, taking to the streets to protest in huge numbers.

Lithuania said on Monday it will ask the International Criminal Court in the Hague to investigate war crimes and crimes against humanity in Ukraine which it says were committed by Russia and its ally Belarus.

Russia warned Kyiv residents to flee their homes on Tuesday and rained rockets down on Kharkiv, as Russian commanders who have failed to achieve a quick victory shifted their tactics to intensify the bombardment of Ukrainian cities.

Elsewhere in Vilnius, graffiti in Russian saying "Russian ship go fuck yourself" appeared on a roof of a building owned by Moscow, referencing the reply of Ukrainian border guards to Russian troops' proposal that they surrender.

In Germany, an artist group painted the slogan "Let's build bridges" stretching over 300 metres on the disused Rahmedetal Bridge near Luedenscheid in western Germany.

"It is important to us that this reaches the people in Ukraine, that they know that other people are also thinking of them and sharing and sympathising," says co-organiser Davis Pahl.

The bridge is due to be demolished in a few months.