(WASHINGTON) — It’s too soon to make “definitive assessments” about the Ukrainian counteroffensive officially underway for more than a week, Gen. Mark Milley, the chairman of the Joint Chiefs of Staff said Thursday, but he also said Ukraine “is making steady progress.”

While Ukraine has sustained some battlefield losses of armored vehicles, including Bradley Infantry Fighting Vehicles, Defense Secretary Lloyd Austin, appearing at a news conference in Brussels with Milley, said Russia is overplaying those losses and that Ukraine continues to have “a lot of combat capability — combat power.”

Referring to Russian social media posts purportedly showing damaged Ukrainian vehicles, Austin said, “I think the Russians have shown us that same five vehicles about 1000 times from 10 different angles,” speaking at the conclusion of the monthly meeting of the more than 50 countries providing military assistance to Ukraine.

“This is war. So, we know that there will be battle damage on both sides,” said Austin. “What’s important is that the Ukrainians have the ability to recover equipment that’s been damaged, repair where possible, get that equipment back into the fight.”

Austin noted that “this will continue to be a tough fight as we anticipated and I believe that the element that does the best in terms of sustainment will probably have the advantage at the end of the day.”

Ukraine’s leaders announced the formal start of a counteroffensive last week that has mostly consisted of probing operations along the 600-mile front along southern and eastern Ukraine that has been under Russian control since last year.

Ukrainian troops have recaptured several small villages in southern Ukraine, but they have encountered what a U.S. official labeled as “tough resistance” from Russian forces.

“Ukraine has begun their attack and they are making steady progress,” said Milley who also cautioned that the counteroffensive is “in the early stages, and it’s far too early to make any definitive assessments.”

Milley explained that it would be “premature” to estimate how long the counteroffensive could last given that “there are several 100,000 Russian troops dug in and prepared positions all along the front line.”

“This is a very difficult fight. It is a very violent fight. And it will likely take a considerable amount of time at high cost,” he added.

A U.S. official told ABC News that the Ukrainian forces involved in the counteroffensive include some of the 60,000 Ukrainian troops that have been trained and equipped by the United States and other countries.

“U.S. training and effort has created 12 maneuver battalions — nearly 5,000 operators — hat are fighting those machines right now,” Milley told reporters.

That training effort continues as three Ukrainian battalions are being trained in Germany, including one that will be trained on the 31 M1 Abrams tanks that will arrive in Ukraine later this year.

Western officials attribute what they call the Ukrainian counteroffensive’s “slow progress” to the large-scale defenses that Russia has set up behind the front lines in anticipation of a major Ukrainian counteroffensive.

Those include hundreds of miles of layered mine fields, trenches, and “dragon’s teeth” to disable tanks that Russia has built roughly 12 to 18 miles from current front lines.

While Ukrainian forces have been able to penetrate some of those front lines the western officials believe that Russian troop losses have been limited by the successful withdrawal of forces.

Although the Ukrainian military has, in areas, managed to penetrate Russia’s initial defensive lines, the Russian military has, when necessary, managed to withdraw forces from areas of the frontline in a relatively successful manner, so far limiting Russian casualties.

Images posted on social media have shown significant damage to German Leopard 2 tanks and American-made Bradleys that were specifically provided to assist Ukraine with its counteroffensive.

But some analysts believe that Ukraine is holding back the bulk of its forces in reserve waiting for the right opportunity of a breakthrough.

“The offensive has clearly started, but not I think the main attack,” according to retired Lt. Gen. Ben Hodges, formerly the top U.S. Army commander in Europe and now a senior adviser to Human Rights First.

Writing in an article for the Center for European Policy Analysis, Hodges speculates that the inclusion of some Leopards on the battlefield in an early fight was possibly “intended to draw a lot of attention to that area, perhaps as a decoy. I cannot know that, but it’s something I would have done, given all the attention in the media about these excellent tanks.”

“When we see large, armored formations join the assault, then I think we’ll know the main attack has really begun,” Hodges said.

“But even then, be careful,” he added. “The Ukrainian General Staff will want to keep the Russians guessing about the location of the main attack for as long as possible, and they won’t be too bothered (and will probably welcome) Twitter getting it wrong.”

Dr. Jack Watling, a senior research fellow at the Royal United Services Institute agrees that Ukraine’s probing operations along the extensive front lines are intended to draw Russia into committing its own reserve forces to back up weak points.

“Once these troops are pulled forwards, it will become easier to identify the weak points in the Russian lines, where a breakthrough will not be met by a new screen of repositioned forces,” he wrote in an article for RUSI.ORG.

As the battle develops Watling believes the great unknown is how the counteroffensive will affect the morale of Russian troops currently fighting from defensive positions.

“If Russian units can be forced to reposition, however, the poor training and discipline of Moscow’s forces could see the defence become uncoordinated and susceptible to collapse,” he wrote.

-ABC News’ Tom Soufi-Burridge and Zoe Magee contributed to this report.

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