Kyiv's Western backers will meet Thursday at NATO headquarters in Brussels to get the latest update from Ukraine's defence minister on the progress of the assaults.

"The most obvious thing is to ensure they have the weapons, the supplies, the maintenance to continue to conduct the offensive," Stoltenberg told journalists.

Stoltenberg said that there was always recognition that Ukraine would suffer losses as it seeks to breach heavily fortified Russian lines.

"There will be casualties, also, when it comes to modern NATO equipment," he said.

"No one expected there to be zero casualties. The realities of this is fierce, fierce fighting."

Stoltenberg reiterated that Ukraine's offensive was making advances, but said "it is still early days and we do not know if this will be a turning point of the war".

NATO allies, spearheaded by the United States, have already funnelled weaponry worth tens of billions of dollars to Ukraine to help it fight off Russia's forces since Moscow launched its war in February 2022.

Those supplies have sapped western stockpiles and sent countries scrambling to try to refill their shelves as Ukraine has fired off thousands of shells a day.

Stoltenberg said he expected NATO defence ministers at a subsequent meeting on Friday to agree to "substantially" ramp up the targets for the amount of ammunition each NATO member must have in stock.

In addition, NATO is also looking to approve a "defence production action plan" at a summit next month in Lithuania's capital Vilnius to try to get Western defence industries to ratchet up output.

So far this year, Stoltenberg said, NATO countries have jointly ordered 155-millimetre shells worth $1 billion.

The weapons surge comes as the European Union -- which shares 22 members with NATO -- has also launched a plan to supply Ukraine with a million shells and bolster industry.

Officials have been wary of duplicating efforts between the two organisations and further pressuring already overstretched manufacturers.