Zelensky says Ukraine achieving 'results' in northeast

Ukrainian troops are achieving "tangible" results against Russian forces in the hotspot northeastern Kharkiv region but the frontline situation is "extremely difficult" elsewhere, President Volodymyr Zelensky said on Tuesday.

Russia launched a fresh assault on Kharkiv on May 10 and has since captured several small settlements in its biggest advance in 18 months.

Moscow on Tuesday also began nuclear weapons drills close to Ukraine in what it said was a response to Western "threats", after Kiev appealed to allies to down Russian missiles from their own territory.

"In the Kharkiv region, our forces are destroying the occupier, the results are tangible," Zelensky said in his evening address.

But he warned the situation on the eastern front near the cities of Pokrovsk, Kramatorsk and Kurakhove remained "extremely difficult".

"Most of the battles are going on there now," he said.

The Russian official appointed by Moscow as governor of the Kharkiv region said Tuesday that his country's forces controlled nearly half of Vovchansk, a town near the border at the epicentre of fighting.

"Our guys control about 40 percent of the city. They have cut deep into the defense and knocked out the enemy as far as they could," said Vitaly Ganchev.

"The northern part of the city has already been completely liberated," he told Russian state television.

A Ukrainian military spokesman told state media that fighting in the border territories "remains difficult and is changing dynamically".

But he also said the number of bouts with Russian forces had decreased.

Zelensky warned last week that the Russian offensive in Kharkiv might be only a "first wave" and that Russian troops could be aiming for Kharkiv city, Ukraine...