Ukraine's military says private mercenary forces fighting for Russia are suffering especially high casualty rates as battles rage in the northeast of the country around Kharkiv.

The General Staff of the Armed Forces said in its battlefield summary on September 7 that the "significant losses" of such private soldiers "account for more than 40 percent of those seriously wounded or killed."

Meanwhile, Ukrainian sources did not provide details but suggested a Ukrainian counteroffensive begun last week was continuing and "enjoying some success."

In a speech to an economic audience in Vladivostok, Russian President Vladimir Putin tried to publicly make the case for the unprovoked attack, saying what Moscow called a "special military operation" was necessary.

"I can say that the main benefit has been the strengthening of our sovereignty, and that is an unmistakable result of what is happening right now," the Russian leader said, adding, "We have lost nothing and we will lose nothing."

Putin claimed, falsely, that Russia hadn't started any military operations but "we are trying to end those that started in 2014."

In 2014, Russian troops covertly occupied Crimea ahead of its forced annexation and Kremlin-backed separatists launched armed insurrections in eastern Ukraine.

It is impossible to immediately confirm either side's claims of battlefield developments in the six-month-old Russian invasion.

But the Ukrainian Army says the Russian side "continues to focus its efforts" on establishing full control over the territory of the eastern Donetsk region and holding onto areas around Kharkiv and occupied southern areas, including Zaporizhzhya around the seized nuclear power plant and Mykolayiv.

It also said Russian troops were battling to hold ground in Kherson, where Ukraine reportedly launched a major counteroffensive last week.

Kyiv has been quiet about how that offensive is faring.

The General Staff claimed on September 7 to be continuing dozens of air strikes on Russian ammunition stockpiles and other areas where the enemy or enemy equipment was concentrated.

A senior Moscow-backed separatist said Ukrainian forces had attacked the Russian-held eastern town of Balaklia, father north, between the cities of Kharkiv and Izyum.

The pro-Kyiv governor of the Luhansk region, Serhiy Hayday, said on Ukrainian television that a "counterattack is under way," adding, "Our forces are enjoying some success. Let's leave it at that."

The Ukrainian Army accused the Russian side of firing mortars, barrel, and rocket artillery in the area around the Zaporizhzhya nuclear plant.

The UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), on September 7 issued a report on security at Zaporizhzhya in which it pleaded urgently for a "nuclear safety and security protection zone" around the Soviet-built nuclear plant, which is Europe's largest.

Russian forces occupied Zaporizhzhya in the early days of the invasion and each side has blamed the other for shelling that has prompted the Ukrainian operating staff to shut down all six reactors.

IAEA head Rafael Grossi told the UN Security Council that "we are playing with fire and something very, very catastrophic could take place."

Russian officials quickly dismissed the call and said they were protecting the plant.

Russian Ambassador Vasily Nebenzya later said of the IAEA proposal that it “is not serious” because the Ukrainians "will immediately step in and ruin the whole thing."

Speaking to the 15-member Security Council, UN Secretary-General Antonio Guterres urged both Ukraine and Russia to avoid military actions directed at the plant and asked Russia to commit "to withdraw all military personnel and equipment from that perimeter and a commitment by Ukrainian forces not to move into it."

With reporting by Reuters