Britain's Ministry of Defence said on Tuesday that there was "a serious level of inaccuracy" in a widely-reported leak of alleged classified U.S. information.

U.S. national security agencies and the Justice Department are investigating the release of dozens of classified documents to assess the damage to national security and relations with allies and other countries, including Ukraine.

"The widely reported leak of alleged classified U.S. information has demonstrated a serious level of inaccuracy," a Ministry of Defence spokesperson said in a statement published on Twitter.

"Readers should be cautious about taking at face value allegations that have the potential to spread disinformation."

Reuters has reviewed more than 50 of the documents, labeled "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 Turkey.

The authenticity of documents in the leaks, which could be the most damaging release of U.S. government information since the 2013 publication of thousands of documents on WikiLeaks, has not been independently verified by Reuters.

U.S. officials have said some documents giving battlefield casualty estimates from Ukraine appeared to have been altered to understate Russian losses.