As many as 354,000 Russian and Ukrainian soldiers have been killed or injured in the Ukraine war which is grinding towards a protracted conflict that may last well beyond 2023, according to a trove of purported US intelligence documents posted online. If authentic, the documents, which look like secret US assessments of the war as well as some US espionage against allies, offer rare insight into Washington's view of one of Europe's deadliest conflicts since World War Two. Reuters has not been able to independently verify the documents and some countries, including Russia and Ukraine, have questioned their veracity, while US officials say some of the files appear to have been altered. One Feb. 23, 2023 assessment, titled "Battle for the Donbas Region Likely Heading for a Stalemate Throughout 2023", says Russia is unlikely to be able to take that part of east Ukraine. "Russia's grinding campaign of attrition in the Donbas region is likely heading toward a stalemate, thwarting Moscow's goal to capture the entire region in 2023," reads the assessment above a classified map of Russian positions. "These tactics have diminished Russian forces and munition stockpiles to a level that, barring an unforeseen recovery, can exhaust Russian units and frustrate Moscow's war aims, resulting in a protracted war beyond 2023." Russia's defense ministry did not respond to a request for comment. Moscow has said it does not know if the documents are real and they may be an attempt to sow discord. According to an assessment collated by the US Defense Intelligence Agency, Russia has suffered 189,500-223,000 total casualties, including 35,500-43,000 killed in action and 154,000-180,000 wounded. Ukraine has suffered 124,500-131,000 total casualties, including 15,500-17,500 killed in action and 109,000-113,500 wounded in action, according to the document entitled "Russia/Ukraine - Assessed Combat Sustainability and Attrition." The figures are around 10 times bigger than any public casualty figures published by either Moscow or Kyiv. Neither side gives timely data on military losses. US wary of stirring China One US document posted on Russian Telegram channels had the casualty figures crudely altered to reduce Russian casualties and increase Ukrainian casualties. Reuters has seen two versions of the same document with one clearly altered. "RUS continues to fall behind stated goals for the replenishment of equipment and personnel to support operations in Ukraine," according to the Defense Intelligence Agency, which stresses there are significant gaps in information. The document on casualties is embossed with emblems of the US Joint Chiefs of Staff and the Defense Intelligence Agency. Both Russia and Ukraine are assessed to have "moderate" combat sustainability - which means that both are likely to be able to continue to fight for some time. The documents show that while Russia has overall numerical superiority in some areas, Ukraine has more tanks and armored personnel carriers (APCs) in theater than Russia. Russia, according to the Defense Intelligence Agency, has lost 2,048 tanks and 3,900 APCs while Ukraine has lost 468 tanks and 1,020 APCs. Ukraine has 802 tanks and 3,498 APCs fielded, while Russia has 419 tanks and 2,928 APCs in theater. Russia has superiority in fighters and air defenses, according to the document on casualties. Reuters was unable to verify the figures, which are at odds with Russian tallies of its destruction of Ukrainian equipment. The US documents also show the concerns in Washington about Ukrainian strikes deep into Russia - and even potentially on Moscow - due to the impact such attacks could have on China's position. "China would respond more strongly and most likely increase the scale and scope of material it is willing to provide Russia if Ukrainian strikes hit a location of high strategic value or appeared to target senior Russian leaders," said what appeared to be a collation of US intelligence assessments. Reuters has reviewed more than 50 of the documents, labelled "Secret" and "Top Secret", that first appeared on social media sites in March and purportedly reveal details of Ukrainian military vulnerabilities and information about allies including Israel, South Korea and Türkiye.