Russian President Vladimir Putin has held a meeting of the country's top brass to discuss boosting security in Crimea after reports of foiled attacks.

Intelligence chiefs said two people were killed fending off what they described as a series of attempted attacks in Crimea by Ukrainian "saboteurs".

Ukraine rejected the claims as "fantasy" and "a provocation".

Russia annexed the Black Sea peninsula in March 2014 following a hastily called referendum, an event that sparked Russian-backed separatists to begin fighting in eastern Ukraine, where deadly fighting is continuing.

The Kremlin said Mr Putin had chaired a Security Council session to discuss "additional measures" to ensure security at Crimea's de-facto border, the territorial waters around it and Crimean air space.

Meanwhile, Ukrainian President Petro Poroshenko says he has ordered the army to be put on combat alert on the de-facto border with Crimea and the line of contact in eastern Ukraine.

Mr Poroshenko's statement comes after Russia accused Ukraine of plotting terrorist attacks in Crimea.

Fighting in eastern Ukraine between government troops and Russian-backed separatists has claimed more than 9,500 lives since it began in 2014. But there have not been any reports of disturbances on Ukraine's de-facto border with Crimea.