The Russian Defense Ministry announced Thursday that two new warships — armed with cruise missiles — of the country’s Black Sea Fleet will begin exercise in the eastern part of the Mediterranean from Aug. 15. The announcement came after Ukraine put its forces on combat alert following Russian President Vladimir Putin’s accusations that Kiev was trying to provoke a conflict over Crimea, which was annexed by Moscow in 2014.

The two warships — Serpukhov and Zelyony Dol — will conduct artillery and missile firing practice as part of the drill, which will also include exercises in communication procedures, assistance to a ship damaged by a hypothetical terrorist attack and interception of a ship carrying “militants,” Russia’s Tass news agency reported, citing the ministry.

“The plan for the exercise envisages tests of the naval personnel’s ability to act in critical situations posing threats to Russia’s military security, including threats of terrorist nature,” the Defense Ministry said in an official statement, obtained by Tass.

Ukrainian President Petro Poroshenko also ordered his security advisers Thursday to bring all units along the Crimean border and in eastern Ukraine to “increased combat-readiness.” Earlier in the day, Putin reportedly summoned officials to discuss “antiterrorist security scenarios at the land border, sea, and in the airspace of Crimea.”

On Wednesday, Putin pledged to take counter-measures against Ukraine, accusing it of sending arms into Crimea to carry out terrorist acts. Putin claimed that Kiev was “practicing terror,” and vowed to “not let such things slide by.”

Ukraine A member of the self-proclaimed Donetsk People's Republic forces stands guard near buildings destroyed during battles with Ukrainian armed forces, at Donetsk airport, Ukraine, June 1, 2016. Photo: REUTERS/Alexander Ermochenko

Ukraine, on the other hand, called the accusations false and asked Russia to provide evidence of the claims.

“If it happened in reality, where are the proofs? Statements, pictures, photos, videos, whatever,” the Ukraine's Ambassador to the U.N. Volodymyr Yelchenko told a meeting of the U.N. Security Council in New York, adding that more than 40,000 Russian troops were massed on the Crimea-Ukraine border, reflecting “very bad intentions.”

Meanwhile, Russian state TV broadcast an apparent confession by a man, who claimed he was part of a Ukrainian Defense Ministry force that was sent into Crimea “to carry out acts of sabotage.” Ukrainian media reports, however, said the man was a former volunteer fighter and was recently associated with a charitable organization.

The diplomatic standoff between Russia and Ukraine continues to worsen amid increasing violence in eastern Ukraine, where pro-Russia separatists have been fighting with Ukrainian government forces for over two years, killing nearly 10,000 people so far.

“This is a very tense time,” Elizabeth Trudeau, a U.S. State Department spokeswoman told reporters in Washington Thursday. “It’s time to take a step back, we’re calling on all sides to reduce.”