CORRECTED-WRAPUP 2-In Russia-Ukraine faceoff, both sides stage combat drills

(Corrects Estonian Prime Minister title in paragraph 6)

* Russia holds exercises in Black Sea, Ukraine near Belarus

* Moscow: Conventional, nuclear forces must be combat-ready

* Russian website posts videos of tank movements

By Alexander Marrow and Pavel Polityuk

MOSCOW/KYIV, Nov 24 (Reuters) - Russia staged military drills in the Black Sea, south of Ukraine, on Wednesday and said it needed to sharpen the combat-readiness of its conventional and nuclear forces because of heightened NATO activity near its borders.

Ukraine, which says it believes Russia may be preparing an invasion, held exercises of its own near the frontier with Belarus. An independent Russian investigative group posted photos and videos it said showed movements of tanks and other military vehicles in southern Russia in the past few days.

The increase of military activity on both sides follows weeks of rising tension that have raised the risk of war https://www.reuters.com/world/europe/qa-what-is-risk-war-between-russia-ukraine-2021-11-23 between the two ex-Soviet neighbours, even though Russia denies aggressive intent and Western intelligence sources have told Reuters they do not see any invasion as imminent.

Ukraine is not a NATO member but the United States and the alliance have signalled their backing for Kyiv in ways that Moscow considers provocative, including through warship manoeuvres this month in the Black Sea and a delivery of U.S. patrol boats to the Ukrainian navy.

British Foreign Secretary Liz Truss told Reuters it would be "a grave mistake from Russia" to attack Ukraine.

Estonian Prime Minister Kaja Kallas said the European Union must make it clear to Russia that there would be a high price to pay if it acted against Ukraine, urging the EU to quickly agree on how to deter Moscow.

In Wednesday's exercises in the Black Sea, Russian fighter planes and ships practiced repelling air attacks on naval bases and responding with air strikes, Interfax reported.

Separately, the news agency quoted Defence Minister Sergei Shoigu as saying the need for Russia to further develop its armed forces was dictated by "the complicated military and political conditions in the world and the growing activity of NATO countries near Russia's borders".

He said raising the armed forces' capabilities, supporting the combat preparedness of nuclear forces and strengthening the potential of non-nuclear deterrence are among the priorities.

Shoigu complained on Tuesday that U.S. bombers had rehearsed a nuclear strike on Russia from two different directions earlier this month, and that the planes had come too close to the Russian border. The Pentagon said these drills adhered to international protocols.