US defense officials said that Ukraine's counterattack campaign has made some progress, but it is not yet possible to confirm that Kiev has achieved success. Illustration photo. (Source: AP)

US Defense Secretary Lloyd Austin and Chairman of the US Joint Chiefs of Staff, General Mark A. Milley, both acknowledged that Ukrainian forces were facing many difficulties and suffering many losses, including casualties in both human lives and tanks and other vehicles.

These difficulties were foreseen, the officials said, adding that the counterattack “could take a considerable amount of time and come at a high cost.”

However, they believe that Kiev will achieve a long-term result. As for Russia, Moscow currently lacks unity in its leadership and has problems with military morale.

According to two US defense officials, for Ukraine to "reap" success in this campaign, there needs to be a commitment of unceasing support and unity from the international community.

In addition, military experts revealed that Ukraine's initial effort was to lure Russian reserve forces to pressured areas, thereby finding weak points in Russia's defense lines.

A senior US defense official said the Ukraine Defense Liaison Group is beginning to discuss ways to leverage Western assistance, particularly military hardware, to make breakthroughs on the battlefield, while also finding ways to help Ukrainian soldiers operate this equipment proficiently.

In recent months, the US and its allies have focused on training Kiev forces how to repair donated equipment.

According to a senior Canadian official involved in the Ukrainian soldier training program, several countries have specific training plans in place by the end of this year.

To date, about 6,000 Ukrainians have participated in 65 training courses, at 40 locations on 3 different continents.

On the same day, June 19, US President Joe Biden warned that the risk of Russian President Vladimir Putin using tactical nuclear weapons "is real".

Mr Biden made the statement just days after condemning Russia for deploying these weapons in Belarus.

Previously, on June 17, Mr. Biden strongly opposed President Putin's announcement that Russia deployed its first tactical nuclear weapons to Belarus.

Meanwhile, Belarusian President Alexander Lukashenko revealed last week that Minsk had begun receiving tactical nuclear weapons from Moscow - said to be three times more powerful than the atomic bombs the US dropped on Hiroshima and Nagasaki (Japan) in 1945.