Ukraine has formally invoked the risk reduction mechanism under the Section III of the Vienna Document, Ukrainian Foreign Minister Dmytro Kuleba has said.

"We have officially triggered the risk reduction mechanism in accordance with para. III of the Vienna Document, and requested Russia to provide detailed explanations on military activities in the areas adjacent to the territory of Ukraine and in the temporarily occupied Crimea," Kuleba said on Twitter on Friday.

"According to the Vienna Document, Russia needs to provide detailed explanation on the objectives, precise location and dates of completion of its military activities, as well as designation, subordination, number of formations, as well as types of equipment involved," Kuleba said on Twitter.

The Minister said Russia has 48 hours to reply.

"In case of absence of reply or its insufficiency/irrelevance, Ukraine will address Russia as well as other participating states of the Vienna Document, in order to convene an extraordinary meeting, where Russia will have to provide explanations. We will keep using all diplomatic means to ensure security of Ukraine," he said.