They said that the vessels had not followed the formal procedure for passage through the strait, that the Ukrainian ships had been manoeuvring dangerously, and that they were not responding to radio communications.

[9][8][25] The Ukrainian president characterised the incident as a potential precursor to a Russian invasion, and declared martial law along the border with Russia and in Black Sea coastal areas, which expired on 26 December 2018.

Ukraine and Russia agreed to the principle of freedom of movement through the strait and the Sea of Azov in 2003 following the Tuzla Island incident.

[14] According to the Defense News, "From Russia's perspective, tensions began flaring in March, when Ukrainian coast guard vessels in the Sea of Azov seized the Nord, a Russian-flagged fishing boat operating out of the Crimean city of Kerch.

[41] In late September, the Ukrainian Navy launched an operation to move the search-and-rescue ship Donbas and the tugboat Korets [uk] from Odesa to Mariupol.

The ships, commanded by Dmytro Kovalenko, Ukrainian Naval Forces Deputy Chief of Staff, radioed their intention to enter the Azov Sea via the Kerch Strait as they approached it on 23 September, but did not follow the official procedure to request permission.

According to Kovalenko, this was an intentional form of "naval diplomacy", carried out with the aim of asserting the Ukrainian claim to the surrounding waters.

[citation needed] EU Commissioner for Security Sir Julian King said that Russia had staged a year-long disinformation campaign in order to "soften up" public opinion in preparation for the incident.

According to King, numerous rumours were spread about the plans of the Ukrainian authorities, including that the Ukrainian government had begun dredging the Azov Sea in preparation for the arrival of a NATO fleet, that it intended to infect the Black Sea with cholera, and that it planned to blow up the Crimean Bridge with a nuclear bomb.

[46] Pavel Felgenhauer, a Moscow-based defense analyst and columnist for Novaya Gazeta, speculated that Putin's government instigated the incident out of concern that Ukraine's naval bases in the Sea of Azov might eventually host visiting NATO patrols.

[9] Agents of the Ukrainian SBU security service were present on board the ships; according to Ukraine they were providing ordinary counter-intelligence coverage.

When the Ukrainians refused, citing the 2003 Russo-Ukrainian treaty on freedom of navigation in the area, the Russian boats attempted to intercept them, and rammed the tugboat Yany Kapu several times.

[48] The Ukrainian naval vessels then continued their journey, stopping near the anchorage 471 waiting zone, about 14 kilometres (9 mi) from the Crimean Bridge, and remained there for the next eight hours.

[9][58][11] In a statement, the Ukrainian Navy said, "After leaving the 12-mile zone, the Russian Federation's FSB opened fire at the flotilla belonging to... the armed forces of Ukraine".

[9] Russia did not immediately or directly respond to the allegation, but Russian news agencies cited the Federal Security Service (FSB) as saying it had incontrovertible proof that Ukraine had orchestrated what it called a "provocation" and would publicise its evidence soon.

[9][19] Ukrainian Navy spokesman Oleh Chalyk said that Yany Kapu had "established contact with a coast-guard outpost" operated by the FSB Border Service and "communicated its intention to sail through the Kerch Strait.

[61] Also on that day, according to APK-Inform, Ukrainian commercial shipping returned to normal operation after the Kerch Strait was reopened to civilian traffic.

[73] In March 2019, Canada, the United States and the EU imposed sanctions on Russian citizens and companies for their participation in the incident and activities in Crimea and separatist-controlled eastern Ukraine.

[82] Oleksandr Turchynov, Secretary of the National Security and Defence Council of Ukraine, reportedly said that the incident was an act of war by Russia.

[87] On 26 November, a day after the incident, lawmakers in the Ukrainian Parliament overwhelmingly backed the imposition of martial law in the country's coastal regions, and those bordering Russia and unrecognised Transnistria.

[97] On 30 November, Ukraine banned all Russian men between 16 and 60 from entering the country for the period of the martial law with exceptions for humanitarian purposes,[6] claiming this is a security measure.

In his opinion, otherwise Russia will fulfill its plan to seize the Sea of Azov and that will de facto legitimize the occupation of Crimea.

[citation needed] In the immediate aftermath of the incident, the Russian FSB security service blamed Ukraine for sparking the clashes, saying their "irrefutable" evidence would "soon be made public".

Foreign Minister Sergey Lavrov said on the next day that Ukraine had violated international legal norms by failing to obtain authorisation for its vessels.

[26] He later called the event "a provocation" and accused the Ukrainian president of staging the incident in order to improve his popularity ahead of the 2019 presidential election.

[28] According to the state-run RIA Novosti, the Russian military planned to send additional S-400 Triumf surface-to-air anti-aircraft missile batteries to Crimea.

Russian first deputy ambassador to the UN, Dmitry Polyanski, said that Russia, being a permanent member of the Security Council, would continue to raise important issues "under the agenda they relate to".

[113] On 27 November, Secretary-General António Guterres expressed in a statement that he was "greatly concerned" about the incident and urged Russia and Ukraine to use "maximum restraint" and "to reduce tensions through all available peaceful means in accordance with the Charter of the UN".

[122] In resolution 433 of 12 December 2018 the European Parliament strongly condemned Russian aggression in the Kerch Strait, demanded the release of all Ukrainian vessels and sailors.

[123] Australia,[124] Canada,[125] the Czech Republic,[126] Denmark,[127] Estonia,[103] France,[128] Germany,[129] Hungary,[130] Latvia,[131] Lithuania,[103] Poland,[132] Romania,[133] Slovakia,[134] Sweden,[135] the United Kingdom,[103][136][137] Norway,[138] and Turkey[139] all issued statements criticising Russia's use of force.