Russian-seized Ukrainian military vessels in a port of Kerch, Crimea, on Nov. 26. Photo: STR/AFP/Getty Images

A Russian coast guard vessel rammed a Ukrainian tugboat in the Sea of Azov Sunday, Nov. 25, setting off a series of increasingly dangerous escalations. Russia blocked the Kerch Strait — the narrow passageway connecting the Sea of Azov to the much larger Black Sea — and detained three Ukrainian vessels and 23 sailors. On Monday, Ukraine’s government imposed short-term martial law.

Why it matters: This weekend's attack opened a new front in Russia’s four-year aggression against Ukraine, which includes the ongoing land war in Ukraine's east and the occupation of Crimea.

Background: Moscow has been harassing commercial ships bound for Ukraine’s ports in the Sea of Azov for months, even though Russia and Ukraine have dual control of the sea according to a 2003 agreement. At least 150 merchant vessels have been detained since May, creating significant losses for Ukrainian ports and shipping companies.

Moscow has at least four possible motivations to escalate the conflict now:

  1. Putin’s approval ratings have slipped 16 points, from 82% in April to 66% in October. In the past, the Kremlin has used foreign interventions to shore up nationalist support for Putin and secure a bump in ratings, as with the 2014 annexation of Crimea and to a lesser extent its 2015 military intervention in Syria.
  2. In May, Russia opened a bridge over the Kerch Strait, connecting mainland Russia to occupied Crimea and further securing its claim to the peninsula. Moscow now seems keen to occupy the sea as well.
  3. Should Russia’s Kerch Strait blockade continue, it would add pressure on Ukraine’s struggling economy. Two major Ukrainian ports — Mariupol and Berdyansk — rely on access through the strait for commercial shipments, which has already been partially restricted by the the Kerch bridge’s height.
  4. Moscow may also have an opportunity to pressure President Poroshenko ahead of Ukraine's presidential elections, since he is deeply unpopular and polling in the single digits.

The bottom line: The conflict in the Sea of Azov is unlikely to lead to a massive military engagement or World War III. But the Kremlin seems confident that it will not pay a high price for low-level military aggression similar to its activities in Ukraine’s east. If the international response is weak, Moscow may see an opening for yet more assertive military strikes in the future.

Alina Polyakova is the David M. Rubenstein Fellow for Foreign Policy at the Brookings Institution.

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