Ukraine's Foreign Minister Dmytro Kuleba tweeted on Wednesday that Russia had evacuated night-shift staff at the Titan chemicals plant in Crimea.
The chemicals producer is in Armyansk in the northern part of the Ukrainian peninsula, annexed by Russia in 2014, about 2 km (1-1/4 mile) from territory under Ukrainian control.
While the West expects Russia to start a major invasion of Ukraine, separatist leaders of two breakaway regions, recognized by Russia as independent states this week, asked President Vladimir Putin for military help, the Kremlin said late on Wednesday.
The Titan plant and the Crimean department of the Russian emergency ministry were not available for comments in the early hours on Thursday.
Russian tanks and armoured personnel carriers were seen in Armyansk in recent days, a Crimean resident told Reuters.
"There is a lot of military hardware. The drill ended but it stayed," the resident said.
Ukraine's foreign minister said the evacuation of the plant was a possible preparation for another staged provocation by Russia.
"Moscow seems to have no limits in attempts to falsify pretexts for further aggression," he wrote.
The military intelligence unit of Ukraine's defence ministry said that 50 Titan employees were evacuated on Wednesday evening. The intelligence unit did not rule out that Russia could stage a "terrorist attack" or "chemical sabotage."
(Reporting by Maria Tsvetkova in Kyiv, Olesya Astakhova and Maria Kiselyova in Moscow; Editing by Leslie Adler and Cynthia Osterman)
