The minefields in southern Ukraine are so dense, the troops trying to liberate the area can only advance "tree by tree," one soldier involved in Kyiv's counteroffensive in the south told CNN. In all his years of service, he said, he's never seen this many mines.

The soldier, who asked to be identified by his call sign "Legion," told CNN he believed the actions by his troops were "quite successful and effective." Yet as he and other Ukrainian soldiers wade through mined areas, encountering heavily fortified defenses and aerial assaults, much of the world seems to think they are moving rather slowly.

Ukraine's Western allies are getting nervous about the fact that the progress of Kyiv's long-awaited counteroffensive is being measured in meters, rather than kilometers. Kyiv's allies are well aware that Ukraine cannot defeat Russia without their help. But the slower than expected pace of the counteroffensive means their support could become increasingly unsustainable if the conflict drags on.

Many of the countries that are supporting Ukraine's war efforts are struggling with high inflation, rising interest rates and sluggish growth. Their leaders -- some of whom are facing elections in the next year and a half -- need to justify the huge amount of resources they've poured into Ukraine when their own voters are struggling to make ends meet. That can become difficult if there isn't much battlefield success to show for it.

For now though, the support appears unfaltering. Multiple Ukrainian and Western officials have admitted that the counteroffensive has so far failed to yield major advances -- but most were quick to add that the slow progress was justified.

The front lines in southern and eastern Ukraine have not moved much over the past months, giving Russian troops plenty of time to dig in and prepare for a counteroffensive.

According to an assessment by the Washington-based think tank Institute for the Study of War (ISW), some of the most strategic sections of the front line are guarded by multiple lines of defense, making it very difficult for the Ukrainians to break through.

Chairman of the US Joint Chiefs of Staff Gen. Mark Milley said that the pace is not surprising, given that Ukrainian soldiers were fighting "for their life."

"We are giving them as much help as humanly possible, but at the end of the day, Ukrainian soldiers are assaulting through minefields and into trenches," he said.

"So yes, sure, it goes a little slow, but that is part of the nature of war," Milley said at the National Press Club on Friday.

Milley stressed that, while slowly, the Ukrainians were pushing ahead. "(The offensive) is advancing steadily, deliberately, working its way through very difficult minefields ... you know, 500 meters a day, 1,000 meters a day, 2,000 meters a day, that kind of thing," he said.

While Ukraine's forces work their way through deadly minefields on the ground, they are still lacking air superiority and are under frequent attacks from above.

Legion, a master-sergeant in Ukraine's 47th Brigade which is involved in the fighting in the south, said it was clear that Russian forces have been preparing for this moment for months.

"They knew that this area is where the main attack will take place, so they prepared thoroughly. They have artillery and aviation here, and both fighters and helicopters are working regularly," he said.

Legion told CNN the fighting in the area was comparable to "what it was like in Bakhmut during the hottest phase."

'Major events ahead'

Ukrainian officials have repeatedly said that while the counteroffensive is under way, the main push is yet to come.

Deputy Minister of Defense Hanna Maliar said last month that Ukraine was holding back some of its reserves and that the "main strike" was still ahead.

ISW also said that information published by Russian military bloggers about the situation along the front lines suggests that "Ukrainian forces are not currently attempting the kind of large-scale operations that would result in rapid territorial advances."

Instead, Ukrainian military appears to be launching smaller attacks in different directions along the nearly 1,000-kilometer-long front line (or 621 miles), trying to exhaust Russian reserves before launching a major push.

Meanwhile, the country's President Volodymyr Zelensky has said he wanted to be strategic about where troops are being sent.

"Every meter, every kilometer costs lives," he said. "You can do something really fast, but the field is mined to the ground. People are our treasure. That's why we are very careful."

Zelensky acknowledged on Monday that last week was difficult for the troops on the front lines. "But we are making progress. We are moving forward, step by step!" he said in a statement.

Milley urged observers to remain patient, saying he expects the counteroffensive to last as long as 10 weeks.

"What I had said was this is going to take six, eight, 10 weeks. It's going to be very difficult. It's going to be very long, and it's going to be very, very bloody. And no one should have any illusions about any of that," he said.