Pro-Russian separatists said on Saturday they had uncovered a plan by Kyiv to seize territory they control in eastern Ukraine by force, and paraded a man they said was a Ukrainian spy.

Authorities in the Ukrainian capital quickly dismissed the alleged plan as a fake and have shrugged off spy allegations in the past, but such reports are contributing to a rise in tension.

Fears are growing in Kyiv and the West that a false-flag operation — an act committed with the intent of pinning blame on another party — could be staged in eastern Ukraine and used as a pretext for Russia to attack.