It's not often that the Vienna Document para 16 is invoked, which happened today in the OSCE, so let's do a recap

Thread 1/10

Per para 16, states "consult and co-operate with each other about any unusual and unscheduled activities of their military forces outside their normal peacetime locations which are militarily significant [...] about which a participating State expresses its security concern" 2/10

First, the state which has concerns about an unusual military activity taking place on another state's territory can send it a request for clarification. The latter needs to respond within 48 hours https://www.osce.org/files/f/documents/a/4/86597.pdf#page=16 3/10

While such request was not previously reported, @usosce states that yesterday (April 9) Russia sent a notification that the U.S. mission believes did not answer questions in Ukraine's request (pic 1) https://osce.usmission.gov/meeting-requested-by-ukraine-under-vienna-document-chapter-iii-regarding-unusual-russian-military-activity/

@GER_OSCE & @RP_France_OSCE state the same (pic 2) 4/10

After considering the reply the concerned state may request a meeting that needs to be held within 48 hours. Either state may invite other states to participate (16.2) or may request a meeting of all participating states (16.3). In any case the meeting is chaired by CiO 5/10

The meeting doesn't have to be public, but today's meeting was publicly announced a few hours before it was scheduled, probably to put some pressure on Russia. Nonetheless, Russia did not participate, while 38 states did 6/10 https://twitter.com/LT_OSCE/status/1380918167858515970

Why didn't Russia participate? Probably, this implies that Russia have already provided all information that it wanted in its response. We don't yet have an official statement, only a comment from @Amb_Ulyanov https://twitter.com/Amb_Ulyanov/status/1380928927842074629 7/

Technically speaking the Vienna Document para 16 text is not very specific about the procedure, e.g. it doesn't mention whether the responding state can decide not to participate in such a meeting and what happens if it doesn't. And the VD is not legally binding 8/10

But political bindedness matters too, so it's not surprising to see statements expressing regret at Russia's non-participation https://twitter.com/PLinOSCE/status/1380905963054583810 9/10

Finally, it's worth mentioning that there's an effort to update the Vienna Document and specifically its Chapter 3 (which includes para 16). But modernization would require consensus, and Russia believes that it's not reasonable in today's confrontational environment 10/10