The US Department of Defense has been observing the Ukrainian Defence Forces' advance as part of a counteroffensive, but predicts it will be a challenging and prolonged struggle.

Brigadier General Patrick Ryder, Pentagon Press Secretary said at a briefing the US continues to see the Ukrainian counteroffensive "move forward", adding that it "has and will continue to be a tough fight" for the Armed Forces of Ukraine (AFU).

The general also emphasised US Secretary of Defense Lloyd Austin's remarks that "this will be a marathon and not a sprint", summing up that Washington is "going to continue to support Ukraine for as long as it takes".

"And so again, our focus is going to be on communicating with them, communicating with our allies and partners to ensure that, as they have needs on the battlefield, that we're able to support them," Ryder pointed out.

Eero Rebo, Chief of the General Staff of the Estonian Defence Forces, suggested that Ukrainian troops were not achieving quick success in the counteroffensive because the forces on the battlefield are on an equal footing.

Earlier, the White House said the Ukrainian counteroffensive was moving slower than planned, but it had not stopped.

The UK MoD stressed that Ukrainian counteroffensive operations were going as planned and that Kyiv was exercising due care by not sending large numbers of people and Western weapons through dense Russian minefields.