Ukraine has issued restrictions on any foreigners crossing from Ukraine to Crimea as part of the martial law imposed on that country for the next 30 days. This move seems primarily targeted at Russians.
Here's what we know
On Sunday, the Russian military seized two Ukrainian naval artillery boats and a naval tug boat. The ships had been trying to pass through the Kerch Strait, the only route between the Black Sea and the Sea of Azov. The strait had previously been designated as a shared region that both nations were free to access, but since Russia annexed Crimea it had claimed sole control of the strait.
Ukraine has said that six sailors were injured when the ships were taken, although Russia insists that it was only three and that they have been given medical assistance.
Following the incident, Ukrainian President Petro Poroshenko asked the Ukrainian Parliament to impose martial law, saying that the country was under threat from “Russian aggression.”
On Monday, the Parliament voted to implement martial law for 30 days. Poroshenko had asked for 30 days following criticism that he would use martial law to postpone the Ukrainian presidential elections in March.
Russia has dismissed the entire debacle as being "undoubtedly a provocation" fabricated by Poroshenko's administration because he had been performing poorly in polls.
As part of the new martial law, Russians living in Ukraine will be hit with travel restrictions, as well as restrictions on bank withdrawals.
About 17 percent of Ukrainians identify as ethnic Russians, and Russian is widely spoken in the eastern and southern regions of the country. While these ethnic Russians are still Ukrainian citizens and presumably would not be hit by the sanctions, this does reflect the close relationship that these border regions have with Russia.
In response to martial law, Russian state media claims that the Russian government has sent surface-to-air missiles to northern Crimea.
Poroshenko has also asked for NATO warships to be sent to the Sea of Azov. Ukraine is not a member of NATO, but the international organization was created to act as a safeguard against Russian aggression in Europe.
However, the only route for ships to enter the Sea of Azov is the Kerch Strait, and the agreement between Russia and Ukraine regarding shared use of the strait specifically states that foreign warships cannot enter the Sea of Azov without the permission of both parties.