Russia on Thursday began drilling for nuclear war in a massive, three-day exercise it asserts was planned months ago, Nezavisimaya Gazeta reports.

Roughly 10,000 military personnel were expected to participate in the maneuvers, which are intended as practice for a large-scale nuclear offensive, according to the Russian newspaper. Exercise participants were set to position and prepare missile-firing units for launch, and to practice various administrative and support functions for the operation, said Col. Igor Yegorov, a Russian Defense Ministry spokesman for the strategic missile services.

Troops were expected to conduct surveillance for chemical, biological and radiological threats, as well as to identify and stop conventional efforts to thwart the offensive.

Russian strategic missile forces chief Col. Gen. Sergei Karakaev first unveiled plans for the command staff exercise in December, Nezavisimaya Gazeta reported. The drill was expected to focus on the Omsk and Orenburg armies of Karakaev's missile forces, and to involve 1,000 pieces of equipment belonging to more than 30 units of the Russian military.

Meanwhile, U.S. government insiders said Russia has positioned soldiers and other assets to potentially support a new push into Ukraine, the Wall Street Journal reported on Friday. Moscow insists it is only conducting practice maneuvers, but the moves heightened Western suspicions amid tensions over Russia's annexation of the Crimea region of Ukraine.

In light of the March incursion, the Obama administration on Thursday announced it would prohibit defense sales to Russia, Reuters reported.

Separately, some U.S. lawmakers urged President Obama to take additional steps targeting Russia's government-run arms firm, the wire service reported on Thursday.

"We call on you to cancel all existing [Pentagon] contracts with Rosoboronexport, as well as any plans for future deals, and impose sanctions to ban contracts with any company that cooperates with Rosoboronexport on military programs," says a statement by Republican Senators Dan Coats (Ind.) and John Cornyn (Texas).