Russian forces have captured four villages in Ukraine’s north-eastern Sumy region after Vladimir Putin ordered his troops to carve out a buffer zone along the border.

The new incursion, which is now gathering steam, comes after days of shelling of the region and some of Russia’s largest aerial bombardments across Ukraine since the beginning of the three-year war.

Ukrainian officials said for weeks that Russian troops were trying to make inroads into Sumy, the region’s main city that lies 18 miles from the border, citing it as evidence that Russia is not serious about peace.

In response to Russia scaling up its attacks, Donald Trump, the US president. accused Putin on Tuesday of “playing with fire” in a fresh tirade against his counterpart over stalled efforts to achieve a ceasefire.

Sergei Lavrov, Russia’s foreign minister, had earlier claimed it was Europe, not Moscow, that was “sabotaging” peace talks as he lashed out against decisions to allow Ukraine to strike Russia with Western-supplied weapons.

A buffer zone in Sumy would reduce Kyiv’s ability to launch drone strikes on Russian territory and guard against any future Ukrainian cross-border attacks.