Russia and Ukraine are ramping up security measures after the Kremlin accused Kiev’s forces of mounting a “terrorist” raid in Crimea, which allegedly killed two of Moscow’s servicemen on the peninsula that it annexed in 2014.

Russian president Vladimir Putin said Kiev had “switched to terror tactics instead of searching for a peaceful settlement” to its conflict with Moscow, which after seizing Crimea fomented a separatist insurgency in eastern Ukraine that has killed some 10,000 people and displaced two million.

“From the Russian side there were losses – two servicemen killed. We obviously will not let such a thing pass,” Mr Putin said, amid numerous reports that Moscow had sent major military reinforcements to Crimea in recent days.

On Thursday morning, Mr Putin convened his security council to discuss “additional security measures to ensure the safety of citizens and vital infrastructure in Crimea,” the Kremlin said.

“Scenarios involving anti-terrorist security measures at the land and sea borders and in the airspace of Crimea were also considered in detail.”

Russia’s defence ministry announced on Thursday that naval ships and helicopters were starting exercises in the Black Sea, where Crimea is located, on “repelling an attack by underwater saboteurs”.

Ukrainian president Petro Poroshenko dismissed Russia’s allegations as “senseless and cynical”, saying “these fantasies are only another pretext for the next military threats toward Ukraine”.

Kiev also denied that a Ukrainian citizen arrested by Russian forces in Crimea had been on a sabotage mission last weekend.

Mr Poroshenko told his diplomats to arrange telephone talks with Mr Putin and western leaders, and at Kiev’s request the United Nations Security Council was expected to discuss developments around Crimea on Thursday.

Combat readiness

Ukraine also announced its own war games in areas near the Black Sea.

“With the support of naval aviation and other aircraft from Ukraine’s armed forces, marines and coastal artillery units will practice defending important pieces of infrastructure, combating enemy paratroopers and destroying sabotage-intelligence groups,” the defence ministry in Kiev said.

Oleh Slobodyan, a spokesman for Ukraine’s border guards, said Russian reinforcements were arriving in Crimea “with more modern equipment, and there are air assault units”.

“Ukrainian units at the administrative line [with Crimea] are ready for any turn of events,” he added.

Since the weekend, mobile phone footage filmed by civilians in Crimea and posted online has shown large military convoys arriving from Russia and moving across the peninsula.

At the same time, Russia dramatically increased security checks on traffic between Crimea and the rest of Ukraine, and officials urged Russian holidaymakers not to use the ferry crossing to the peninsula because of huge delays.

‘False accusations’

Analysts said Moscow could be testing the West’s support for Kiev, as EU unity on sanctions against Russia weakens and the bloc faces a refugee crisis and Brexit, and the US focuses on an increasingly divisive presidential election campaign.

In addition, Mr Putin might be emboldened by a boost from a sudden rapprochement with Turkey, and he may want to strengthen his hand in talks with the West over the continuing Syria conflict.

He might also want to tighten security in Crimea – and remind voters of perceived security threats – ahead of Russia’s parliamentary elections next month.