Leaked US military documents indicate that the UK has deployed as many as 50 special forces to Ukraine. The documents suggest that more than half of the western special forces personnel present in Ukraine between February and March this year may have been British. It is unclear what activities the special forces may have been engaged in or whether the numbers of personnel have been maintained at this level. The UK’s elite military forces, whose activities are normally shrouded in secrecy, comprise multiple units including the Special Air Service (SAS). The UK government has not disclosed since the beginning of the war that special forces have been active in Ukraine. Prior to Russia’s invasion, in June 2021 the UK embassy in Kyiv said its special forces had conducted training activities with Ukrainian forces. The Ministry of Defence (MoD) declined to comment on the disclosures or answer questions about UK personnel in Ukraine in recent months. However, in a tweet the department said the leak has “demonstrated a serious level of inaccuracy”. The leaked documents, which have not been verified, are part of a tranche of classified US military and intelligence files that were posted on Discord, a platform used by gamers. At present, the original source of the files remains unknown. In recent days, the documents, which are now circulating on social media and in online discussion forums, have prompted a series of media reports about US military and intelligence assessments, primarily about the war in Ukraine. Although some of the files shared online appear to have been doctored, US news outlets including the New York Times have reported that US officials acknowledge many of the documents are genuine and were initially shared online without alterations. The Guardian has reviewed a portion of the leaked documents, which contain photographs of at least two “daily updates” relating to Russia’s invasion of Ukraine. Markings on the documents suggest they were prepared for senior US defence officials. Labelled “secret”, the two daily updates appear to have been created in February and March this year. They contain updates about military operations, logistics, weapons deliveries and training of Ukrainian forces by the US and its Nato allies. In one section, titled “US/NATO SOF in UKR”, the documents appear to list the number of western special forces present in Ukraine. The documents appear to be dated February and March 2023. According to the files, US officials assessed at the time that of the 97 special forces from Nato countries active in Ukraine, 50 were British. This is considerably higher than the number from the US and France, which were said to have deployed 14 and 15 special forces respectively. The documents appear to offer a partial snapshot of US military assessments of the state of the war and allies’ support for Ukraine. They do not contain any information about the purpose of the deployments of UK or other contingents of special forces. The documents suggest the special forces could form part of a Nato special forces command coordinated by the military alliance’s special operations headquarters, but precise details of how the forces are organised are not specified. The UK’s special forces include the SAS, the Special Boat Service, the Special Reconnaissance Regiment, as well as several other secretive military units such as the 18 (UKSF) Signals Regiment. The units, which conduct undercover operations as well as covert surveillance and reconnaissance operations, are the UK military’s most secretive organisations. Unlike the intelligence services, the special forces are not subject to external parliamentary oversight.