Ukraine's president demanded Monday that Russia immediately release Ukrainian sailors and vessels seized in a standoff around Crimea that sharply escalated tensions between the two countries and drew international concern.
The two neighbors have been locked in a tense tug-of-war since Russia's 2014 annexation of Crimea, but the incident late Sunday, in which Russian coast guard ships fired on Ukrainian navy vessels near the Kerch Strait, directly pitted the two militaries against each other, placing them on the verge of an open conflict.
The Ukrainian navy said six of its seamen were wounded when Russian coast guards opened fire on three Ukrainian ships near the Kerch Strait and then seized them. Russia said that three Ukrainian sailors were lightly injured and given medical assistance.
Ukraine's president, Petro Poroshenko, chaired an emergency meeting of his Cabinet early Monday and asked parliament to introduce martial law for two months in response to what he described as Russian aggression.
"We consider it as an act of aggression against our state and a very serious threat," the president said. "Unfortunately, there are no 'red lines' for the Russian Federation."
Ukrainian Foreign Minister Pavlo Klimkin told reporters later Monday that Kiev believes that what happened near the Kerch Strait was no accident but "deliberately planned hostilities."
If adopted by lawmakers, the emergency measures proposed by Mr. Poroshenko will include a partial mobilization and strengthening of the country's air defense. They also include a plethora of vaguely worded steps such as the "strengthening" of anti-terrorism measures and "information security."
The fate of the Ukrainian seamen was not immediately clear. Mr. Klimkin insisted that they should be treated as prisoners of war while Kremlin spokesman Dmitry Peskov did not say what legal status they have.
An emergency meeting of the United Nations Security Council was also called for Monday. The European Union and NATO called for restraint from both sides.
Poroshenko had a phone call Monday with NATO Secretary-General Jens Stoltenberg to discuss the situation. NATO later said that at Poroshenko's request, its ambassadors and Ukraine's envoy will hold emergency talks in Brussels later Monday.
NATO said Mr. Stoltenberg expressed the US-led military alliance's "full support for Ukraine's territorial integrity and sovereignty, including its full navigational rights in its territorial waters under international law."
Poroshenko said at a meeting of Ukraine's national security council Monday that "we demand that [the ships and crews] are urgently turned over to the Ukrainian side" and called for a "de-escalation" of the crisis around Crimea.
Russia and Ukraine have traded blame over the incident that further escalated tensions that have soared since Russia annexed Ukraine's Crimean Peninsula in 2014 and backed a separatist insurgency in eastern Ukraine with clandestine dispatches of troops and weapons.
Ukraine said its vessels were heading to the Sea of Azov in line with international maritime rules, while Russia charged that they had failed to obtain permission to pass through the Kerch Strait separating Crimea from the Russian mainland.
The narrow strait is the only passage between the Black Sea and the Sea of Azov. It's spanned by a 11.8-mile bridge that Russia completed this year. While a 2003 treaty designates the Kerch Strait and Sea of Azov as shared territorial waters, Russia has sought to assert greater control over the passage since the annexation of Crimea.
"There is no doubt that it was done by blessing or, perhaps, even a direct order from the top," said Russian Foreign Minister Sergey Lavrov. "While planning that provocation, Ukraine had undoubtedly hoped to get additional benefits from the situation, expecting the US and Europe to blindly take the provocateurs' side."
He urged the West to "calm down those in Ukraine who are trying to unleash a military hysteria to get political gains in connection with the planned elections" – a reference to Ukraine's presidential vote in March.
A motion to introduce martial law requires a simple majority of votes in the 450-seat parliament, which Poroshenko's party controls. If martial law is introduced as proposed for 60 days, it will derail the presidential election campaign, which was expected to start on Dec. 30 with the vote in March.
Some lawmakers lashed out at Poroshenko's move as an attempt to influence the vote. Polls show Poroshenko trailing far behind arch-rival Yulia Tymoshenko.
"Martial law in Ukraine would present a wonderful chance to manipulate the presidential elections," said Oksana Syroid, a deputy speaker of parliament who is a member of the Samopomich faction.
She noted that martial law was not introduced in 2014 or 2015 despite large-scale fighting between Ukrainian forces and Russia-backed separatists in the east.
President Vladimir Putin's spokesman, Mr. Peskov, said that Poroshenko's initiative to introduce martial law "clearly smacks of electoral intrigues."
"We believe that it's wrong and dangerous to solve electoral tasks by waving a flag of war," he said.
Meanwhile, hundreds of protesters from far-right party National Corps waved flares in the snowy streets outside the Ukrainian parliament Monday. They brandished yellow-and-blue flags with the Ukrainian national symbol, the trident, and a huge white banner reading 'Don't back down!' "
This story was reported by The Associated Press. Additional reporting by Yuras Karmanau in Minsk, Belarus, and Nataliya Vasilyeva in Moscow.