There is mounting evidence that Ukraine has been taking heavy casualties in its counteroffensive, which began roughly ten weeks ago.
ABC News spoke with two former U.S. soldiers who are contracted in a special forces division of the Ukrainian military and who were both injured during an operation in eastern Ukraine two weeks ago.
Both soldiers are currently in a hospital in Kyiv but said they hope to be transferred to Germany for surgery this week in order to remove shrapnel from their bodies.
The men said their team's mission was to seize control of a village on the outskirts of Donetsk city, which has been occupied by a Russian-controlled militia since 2014.
One of the men, a former U.S. soldier from Texas who goes by the callsign "Tango," said his unit of "dozens" of men took "85% casualties" and that two of their comrades were killed when the team was ambushed whilst advancing into Russian-occupied territory. Forty percent of the unit was so badly injured they were rendered "combat ineffective," he said.
The other U.S. army veteran, who goes by the callsign "Goldfish" said it was immediately apparent that they were up against "very organized resistance" from Russian troops.
"It was definitely a very professional force that we were fighting against," the U.S. army veteran from Alaska said.
He spoke to ABC News in his hospital room in Kyiv which he was sharing with three other wounded Ukrainian soldiers.
ABC News also contacted two other Ukrainian soldiers interviewed in earlier phases of the war and they said they have also been injured in the past few weeks.
A Western man, with years of military experience, who is also now contracted with the Ukrainian military, said he sustained a serious injury in the early phase of the counteroffensive in June.
Speaking to ABC News on the condition of anonymity, the soldier said offensive operations which he had been part of were disorganized, criticizing some tactical decisions.
"We lost three Leopards (advanced German-made tanks) in one day because they were just told to drive forward into a minefield," he said.
He added that newly mobilized Ukrainian soldiers often appeared to lack the necessary training for complicated offensive operations on the battlefield.
The soldier, who joined the Ukrainian military more than a year ago, said dozens of men from his battalion had been involved in offensive operations since the beginning of June and around 80% of those men had been injured. However, he added that there had been no fatalities.
He claimed western military equipment such as U.S.-supplied Bradley infantry fighting vehicles were not being used to their full potential because some Ukrainian soldiers didn't have the necessary training or experience.
"It seems like they (Ukrainian soldiers) have been taught to use them but not to employ them (effectively) in a tactical sense (on the battlefield)," he said.
However, the two Americans interviewed by ABC News disagreed with that assessment.
Despite their injuries sustained during their failed mission two weeks ago, they argued that the Ukrainian counteroffensive is being well-executed and heavy casualties in a major military offensive of this nature, against entrenched Russian defenses, are to be expected.
"It's not going to be quick and decisive", the soldier with callsign "Tango" said.
"That's not how counteroffensives work. They (the Ukrainians) are taking casualties. That is normal," he added. "I think it's going well and on pace."
His comrade "Goldfish" said it had been "a very hard fight" for Ukraine.
"But it's a fight that the Ukrainians are fighting very well," he said.
Ukraine has not published casualty figures since Russia launched its full-scale invasion in February of last year.
However, a senior Ukrainian official described the situation as "really tough" with "very intensive fighting on the battlefield".
He added that 80% of casualties were being caused by Russian artillery.
The official said the war was now in a "decisive phase" and insisted that Ukraine needed even more military support from the United States and its partners, including American long range ATACMS missiles, which have a range of 190 miles.
Ukraine has promised the United States that it would only use the missiles to strike Russian assets in occupied parts of Ukraine, and not hit targets inside Russia. However, the Biden Administration has so far refused to supply the long-range missiles.
The senior official insisted that Ukraine urgently needed more military aid in order to help it achieve its goals on the battlefield, arguing that supplying more support now would be a more cost-effective way of holding Russia back and, in turn, guaranteeing security in Europe.