Ukraine's commander-in-chief Oleksandr Syrsky said Saturday the situation on the eastern front had worsened in the face of a heightened Russian offensive.

Syrsky, who took over as commander-in-chief in February after Ukrainian President Volodymyr Zelensky fired his popular predecessor, Valery Zaluzhny, also said Russian forces had superior weapons and numbers.

"The situation on the eastern front has deteriorated significantly in recent days," said Syrsky.

He spoke of "a significant intensification of the enemy's offensive after the presidential elections in Russia" last month and added decisions were being taken "to strengthen the most problematic defence areas with electronic warfare and air defence".

Ukraine has said the situation around the eastern frontline city of Chasiv Yar is "difficult and tense" with the area under "constant fire".

Chasiv Yar lies 20 kilometres (12 miles) west of Bakhmut, which was flattened by months of artillery fire before it was captured by Moscow last May.

Russia has recently secured its first territorial gains since seizing Bakhmut and is now trying to press onwards against Ukrainian units hobbled by delays in the supply of vital Western military aid.

"The enemy is actively attacking our positions in the Lyman and Bakhmut sectors ... In the Pokrovsk sector, they are trying to break through our defence using dozens of tanks and armoured personnel carriers," Syrsky said.

"The issue of achieving technical superiority over the enemy in high-tech weapons has again arisen. Only this will enable us to defeat a larger enemy, he said.

- Training push -

"The second serious problem is to improve the quality of training of military personnel, especially infantry units, so that they can make the most of all the capabilities of military equipment and Western weapons," Syrsky added.

European allies of Ukraine are engaged in a training push for its forces.

France's defence minister Sebastien Lecornu on Friday said future Ukrainian fighter pilots likely to fly American F-16 aircraft were receiving their initial training in the south of France.

Other countries including the Netherlands, Denmark and Romania are seeking to help Ukraine train pilots.

Some Ukrainians, after receiving initial training in Britain, are now undergoing "advanced training" in an undisclosed location to learn how to fly fighter jets, according to a military source.

The issue of Western training for Ukrainian forces comes with US officials Friday having released intelligence purporting to indicate that China is helping Russia undertake its biggest military expansion since Soviet times.

A senior US official said on Friday that China was helping Russia on the joint production of drones, space-based capabilities and machine-tool exports vital for producing ballistic missiles to revitalise Russia's defence industrial base "which had otherwise suffered significant setbacks" since the invasion of Ukraine.

The UN's migration chief Amy Pope meanwhile urged more humanitarian support for Ukraine, saying its needs were "huge" with more than 14 million Ukrainians, or around 40 percent of the population, needing aid.