Ukrainian authorities requested a meeting with members of the Organization for Security and Co-operation in Europe (OSCE) and Russia in the next 48 hours to talk about the Russian military buildup near the border with Ukraine and inside annexed Crimea.
Tensions have been mounting for weeks over the buildup near Ukraine. Washington has said an invasion could happen anytime. Moscow denies planning an invasion and has accused the West of hysteria.
Ukrainian Foreign Minister Dmytro Kuleba said Moscow had not responded after Kyiv on Friday invoked a part of the Vienna Document, a set of security agreements, to demand Moscow explain its military activities.
"Consequently, we take the next step. We request a meeting with Russia and all participating states within 48 hours to discuss its reinforcement & redeployment along our border & in temporarily occupied Crimea," Kuleba tweeted.
"If Russia is serious when it talks about the indivisibility of security in the OSCE space, it must fulfill its commitment to military transparency in order to de-escalate tensions and enhance security for all," he said.
Ukraine has been plagued by conflict in its eastern regions since March 2014, following Russia's invasion and annexation of Crimea.
Russia has also accused Western countries of undermining its security by NATO's expansion towards its borders.
The Kremlin also issued a list of security demands to the West, including a rollback of troop deployments from some ex-Soviet states and guarantees that Ukraine and Georgia would not join NATO.
Meanwhile, Russia said it was concerned by the OSCE's decision to relocate some of their Ukraine-based monitors.
The OSCE "informed the participating states of the decision by 'a number of countries' to relocate their national staff of the OSCE Special Monitoring Mission to Ukraine 'due to deteriorating security conditions,'" Russian Foreign Ministry spokesperson Maria Zakharova said.
"These decisions cannot but cause our serious concern."
The OSCE has served as the world's eyes and ears for the eight-year conflict across Ukraine's Russian-backed separatist east that has claimed more than 14,000 lives.
Weeks of tensions over Ukraine have seen Russia nearly surround its western neighbor with more than 100,000 troops, with Washington warning that an all-out Russian invasion could begin "any day."
Zakharova said the OSCE move further inflamed tensions over Ukraine, adding that the monitoring mission could be used as a "tool" to stage a possible provocation.
"We call on the OSCE leadership to resolutely stop attempts to manipulate the mission and prevent the organization from being drawn into dirty political games," Zakharova added.
Images on social media showed convoys of its white SUVs leaving various parts of the conflict zone because of the staff's need to comply with their respective governments' travel advisories.
