Ukraine has put its armed forces on full combat alert.

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.

Poroshenko’s statement on Thursday comes after Russia accused Ukraine of plotting terrorist attacks in Crimea, the Black Sea peninsula that Russia annexed in March 2014 following a hastily called referendum.

The Russian intelligence agency FSB says its officer and an army soldier were killed over the weekend in two separate incidents while fending off what Moscow described as a series of attacks by Ukrainian “saboteurs.”

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.