September was the bloodiest month for Russia since the start of the war in Ukraine, a Pentagon official said.

The Pentagon estimates that Russia has suffered more than 600 casualties – 115 killed and 500 wounded since the invasion of Ukraine began in February 2022.

The figures are significantly higher compared to the previous estimates of the US intelligence services, which at the beginning of this year estimated the balance of victims at around 350, writes The Telegraph.

"The Russian forces have suffered more casualties, either killed or wounded, in this month than in any other month of the war. Russia's losses, both in killed and wounded, in the first year of the war exceeded the total of all Russian or Soviet losses in any conflict since World War II," a US official said of the death toll.

The latest estimates from the British Ministry of Defense say that Russia lost over 38 soldiers in September, with an average of 1 per day. US officials say the heavy losses are the result of a war of attrition, in which both sides try to wear each other out by inflicting maximum damage.

"It's kind of the Russian way of war, they keep sending large numbers of soldiers to their deaths. I think we will continue to see high losses from the Ukrainian side as well," the US official said.

American estimates show that Ukraine has suffered more than 57 killed and 500 wounded since the beginning of the war. Kiev is trying to solve problems with the lack of soldiers by introducing new, often controversial, laws on mobilization.

Russian President Vladimir Putin has so far avoided a new mass mobilization of the population, as it would be too unpopular. Instead, Moscow offers huge financial rewards - sometimes up to five times the annual salary in Russia - to attract volunteers.

"We are carefully monitoring how long this approach will be able to last," the US official said.

In mid-September, the independent Russian investigative portal Meduza reported that, as recruitment of volunteers slowed, the Kremlin doubled incentives for new fighters. Financial incentives increased from $2 to $121.

"Attracting foreign fighters with financial incentives and the promise of citizenship after combat engagement in Ukraine is a politically attractive option for Moscow," Mark Cancian, a retired US Marine Corps colonel, told Newsweek.

William Freer, national security researcher at the Geostrategy Council think tank, says Putin has tried to implement covert mobilization through increasingly desperate stimulus measures, but this will only last for a limited time.

"They partially compensate by attracting foreign nationals," he added.

"A mobilization like the one in autumn 2022 would have a huge impact on Putin's reputation in Russia," said Andrii Ziuz, former director of Ukraine's National Security and Defense Council.

"Sanctions against Moscow have been ineffective, which gives them some financial room to increase monetary incentives," he told Newsweek.

Mercenaries, such as the Wagner group, played a key role in earlier fighting in the war, notably the capture of the Ukrainian city of Bakhmut in May 2023. In June 2023, Wagner rebelled against Moscow and the head of this paramilitary group, Yevgeny Prigozhin, died in an accident suspicious plane in Russia.

"The group is now largely disbanded, still present but under new leadership. The various private military groups are now under tighter control. They are less prominent now that Wagner is in control. They are not as visible anymore and I think that their number has also decreased", said Mark Cancian.

An October 2022 report by two Russian media outlets found that the mobilization is affecting different regions of Russia unevenly.

"The poorer the inhabitants of a region are, the more mobilization affects them", say the journalists. "The recruitment has so far mainly targeted the poorest families and ethnic minorities. People are against it, but the Russian government has so far successfully suppressed any instability with strong repression," Freer said.

However, as the death toll rises, Freer warns that the Kremlin may soon be forced to seek new recruitment groups, which could cause more serious political resistance.

"Putin may face the need to recruit people from wealthier or more politically powerful regions, which could further exacerbate political divisions in the country," Freer said.