Ukraine ratcheted up tensions with Moscow on Wednesday by warning the Kremlin its army intended to hold two days of missile-launching exercises near the border with Russian-annexed Crimea.

The tests set for Thursday would almost certainly further damage relations between two former Soviet neighbours that treat each other as open foes.

Such exercises near the Crimean peninsula would be a first for Ukraine and it was not immediately clear what sparked their preparation.

Ukraine also failed to say whether the tests would involve specific targets or if the missiles would only be fired into the air.

They come after Moscow last week arrested an alleged spy for the Ukrainian military in Crimea and accused Kiev of abducting two Russian servicemen from the region.

Kiev says Russia illegally annexed the Black Sea peninsula in March 2014 following the preceding month's ouster of Ukraine's Russian-backed president.

It also accuses Moscow of backing a 31-month pro-Russian insurgency in Ukraine's industrial east in a conflict that has claimed nearly 10,000 lives.

Russia calls its takeover of Crimea legal and denies either plotting or backing Ukraine's bloodiest conflict since World War II.

Ukraine's Deputy Defence Minister Oleksandr Dublyan said the missile test launches would begin on Thursday in conformity with international law.

"We are not violating a single international norm," the Dzerkalo Tyzhnya news website quoted Dublyan as saying.

Kiev and the overwhelming majority of the international community consider Crimea -- a mostly Russian-speaking resort region of around two million people -- to be part of Ukraine.

Moscow-based RIA Novosti state news agency earlier quoted Russia's civil aviation authority as saying that Ukraine's missiles would even approach the Crimean capital of Simferopol.

Kiev's media was full of speculation that Russia intended to shoot down the Ukrainian missiles once the tests begin.

Ukraine's national security council chief warned that such threats would not work.

"Threats to use weapons against Ukraine are an effort to turn the hybrid war that Russia has been waging against us for the past three years into an active war," Oleksandr Turchynov said in a statement released to reporters.

But Russian President Vladimir Putin's official spokesman kept to a more cautious line.

"The Kremlin would not like to see any sorts of actions from Ukraine that contradict international law," Dmitry Peskov told reporters in Moscow.

He added that the tests could "create dangerous conditions for international flights crossing the territory of Russia and neighbouring regions".

burs-zak/am/ric