Ukraine accuses Russia of plotting unrest amid Crimea tensions

It also accused Russia of increasing its forces, replenishing munitions and building up military hardware in war zone

Ukraine today accused Russia of plotting further unrest as the international community sought to ease tensions after the two sides ramped up security around the disputed Crimean peninsula.

Russia's FSB security service has said it thwarted "terrorist attacks" in Crimea over last weekend by Ukrainian military intelligence and beaten back armed assaults, claims Kiev has fiercely denied.

Both sides in response have boosted security around the region as the simmering feud sparked by Moscow's annexation of Crimea in March 2014 has unexpectedly flared up again, prompting fears of a wider conflict.

Ukrainian troops near Crimea and along the frontline with pro-Russian separatists in two other eastern regions have been placed on high alert, and Kiev's military intelligence said "the enemy is planning large-scale provocative actions".

It also accused Russia of increasing its forces, replenishing munitions and building up military hardware in the war-scarred east of Ukraine.

Prime Minister Dmitry Medvedev followed up angry accusations from President Vladimir Putin by branding Kiev's alleged raids in Crimea "a crime against the Russian state and the people of Russia".

He warned that Putin could sever diplomatic ties with Ukraine if "there remains no other way to influence the situation", Russian news wires reported.

Russia's military also said it has delivered its most advanced S-400 air defence system to Crimea after pledging to deploy it there last month. The system will become fully operational in December, it said.

Ukraine's security service has raised its terrorist threat level to the highest around Crimea and the eastern regions of Donetsk and Lugansk, where pro-Russian rebels have been fighting government troops for more than two years.

Kiev's alleged attempts at armed incursions into Crimea saw a Russian security service officer killed in clashes while arresting "terrorists" at the weekend, Moscow said.

And Russian soldier died in a firefight with "sabotage-terrorist" groups sent by the Ukrainian military on Monday.

Ukraine's national security council chief Oleksandr Turchynov today dismissed the claims, saying Moscow was trying to cover up deadly shootouts between Russian forces "who traditionally abuse alcohol."

In a move that was likely to add fuel to the dispute Russian state TV aired footage of the interrogations of several alleged infiltrators the authorities claimed to have captured and confessed to having worked for Ukraine's military intelligence.