Ukrainian President Petro Poroshenko has said he had instructed all military units near Crimea and in the easterly Donbass region to be at the highest level of combat readiness as tensions between Kiev and Moscow spill over owing to claims of an incursion into disputed peninsula.

Kiev says Russia is trying to justify escalating a military build-up by making accusations that Ukrainian agents had engaged in terror tactics in Crimea.

On Thursday 11 August, Russian president Vladimir Putin held a meeting with his security council after Moscow said that two Russian servicemen were killed by Ukrainian intelligence officers in a covert operation in the Black Sea territory.

The news agency TASS reported that Putin held the talks "to discuss additional measures of ensuring security of citizens and critical infrastructure facilities of Crimea" after the Russian president had accused Ukraine's government of "terror."

Earlier, in a statement, Poroshenko said: "Russia accusing Ukraine of terrorism in occupied Crimea sounds as senseless and cynical as the statement by Russian leadership that there are no Russian troops in eastern Ukraine."

But Ukraine's ambassador to the European Union, Dmytro Kuleba, said in a Facebook post: "This is not a casus belli yet, but Russia is actively accumulating stories for casus belli."

Also, in a website statement, chairman of Ukraine's National Security and Defence Council, Oleksandr Turchynov, said: "To further escalate the conflict, Putin couldn't imagine anything better than a cheap theater performance by the FSB."

Ukrainian political analyst Vadim Karasev told the newspaper Vedemosti that both Moscow and Kiev had wanted to use the situation to distract their citizens from economic difficulties and that the bilateral relations will be further destabilized, resulting in an "escalation of the hybrid Cold War."

There were even claims in the state-run Russian press that the incident may have been used by Ukraine to hurt Crimea's tourism sector.

However, the independent military expert Anton Lavrov told the newspaper RBC, which is a non-Kremlin news source: "The situation in the Donbass will not be aggravated by the initiative of Moscow because of the lack of readiness of the Russian military to escalate the situation."

"There are no field camps to support the separatists on the border with Eastern Ukraine," he added.