Leaked military documents indicate that Russia's minimum criteria for using tactical nuclear weapons is lower than Moscow has ever publicly admitted, according to experts who reviewed and verified the documents, the Financial Times reported Wednesday.

The criteria range from an enemy invasion of Russian territory to more specific triggers, such as the destruction of 20% of the nation's strategic ballistic missile submarines.

Other potential conditions for using nuclear weapons include the destruction of three or more large surface warships, three airfields, 30% of its nuclear-powered attack submarines, or a simultaneous strike on main and reserve coastal command centers, according to the report.

The documents, which include 29 Russian military files from between 2008 and 2014, also demonstrate a distrust of Beijing, despite improving relations between Russia and China.

For example, training materials demonstrate that Russia's eastern military district carried out exercises that anticipated a hypothetical attack by Beijing.

The Kremlin continues to carry out military exercises near China, including ones conducted in both June and November last year in regions bordering China using nuclear-capable missiles, according to the report.

On the other hand, Russia likely has a higher threshold for using tactical nuclear weapons against Ukraine due to concerns it would likely "escalate the conflict and lead to direct intervention by the U.S. or U.K.," William Alberque, director of strategy, technology, and arms control at the International Institute for Strategic Studies, told the Times.

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