Russia fired on and seized three Ukrainian naval ships on Sunday as they attempted to pass through the narrow Kerch Strait into the Sea of Azov, which lies between Russia and Ukraine.
With relations still raw after Russia's annexation of Crimea in 2014 and its backing of a pro-Moscow insurgency in eastern Ukraine, the incident risks pushing the two countries towards a wider conflict and is likely to renew Western calls for more sanctions on Moscow.
Here is a summary of what happened:
* Russia's Federal Security Service (FSB) patrol ships attempted to stop three Ukrainian naval ships from entering the Sea of Azov via the Kerch Strait on Sunday morning.
* Russia blocked passage into the sea by situating a cargo ship under the road bridge under its control that it opened earlier this year to connect Russia's southern regions to the annexed Crimean peninsula.
* The Russian ships opened fire on the Ukrainian ships, wounding several sailors.
* One of the Ukrainian ships was also rammed by a Russian vessel.
* Russia subsequently seized the three Ukrainian vessels and reportedly towed them to the Crimean port city of Kerch.
The immediate reactions:
* Russia's FSB said it had been forced to act because the ships had illegally entered the country's territorial waters and ignored warnings to stop while maneuvering dangerously.
* The FSB said that the three Ukrainian ships had been heading for the Kerch Strait without having Russian permission to enter, thereby violating border laws.
* According to the Ukrainian navy, the Russian side was notified in advance of the ships’ movement from Odessa to Mariupol, a Ukrainian port city on the Sea of Azov.
* Ukraine denied its ships had done anything wrong and accused Russia of military aggression.
* The Ukrainian Navy said that when the three vessels had attempted to depart back towards Odessa, the Ukrainian ships were fired upon by the FSB border guards.
* Ukraine's navy said that six of its sailors had been injured in the incident. According to an FSB statement cited by Russian state media, three Ukrainian soldiers were wounded. On Monday morning, photos circulated of the captured Ukrainian ships arriving to Kerch.
* On Monday morning, Russia announced the resumption of civilian traffic on the Kerch Strait.
* Russia's human rights ombudsman Tatyana Moskalkova said that Russia had detained 24 Ukrainian sailors in the incident, with three being treated for minor injuries at a Crimean hospital, Interfax reported.
* The Foreign Ministry accused Ukraine on Monday of deliberating provoking an incident in the Kerch Strait in order to create a pretext for new sanctions to be imposed on Moscow. The ministry’s spokeswoman said Ukraine’s charge d’affaires in Russia had been summoned over the “aggressive and provocative action.”
* The FSB called the incident a provocation intended “to create a conflictual situation in the region.”
* Deputy Foreign Minister Grigory Karasin accused Ukrainian President Petro Poroshenko of provoking the incident as part of his campaign to be re-elected as president next March.
* Alexei Navalny, Russia’s leading opposition activist, linked the incident in Kerch with Putin’s falling approval ratings.
* Foreign Minister Pavlo Klimkin said Ukraine reserves the right to defend itself against Russia and does not rule out Moscow committing further acts of aggression either on land or at sea.
* President Poroshenko signed a decree on Monday to introduce martial law for 60 days, a statement on his website said, though it needs parliamentary approval to come into force.
* The Chief of the General Staff issued an order to bring the country’s military on full alert.
* NATO called on "Russia to ensure unhindered access to Ukrainian ports in the Azov Sea, in accordance to international law.”
* EU Spokesperson for Foreign Affairs Maja Kocijancic issued a statement urging the parties "to act with utmost restraint to de-escalate the situation immediately" and said the bloc expected "Russia to restore freedom of passage at the Kerch Strait."
Reuters contributed reporting.