Crimea standoff sharply escalates tensions between Russian and Ukraine
Ukraine's president has demanded that Russia immediately release Ukrainian sailors and ships seized in a standoff around Crimea that sharply escalated tensions between the two countries.
The neighbours have been locked in a tense tug-of-war since Russia's 2014 annexation of Crimea, but the incident in which Russian coast guard ships fired on Ukrainian navy vessels directly pitted the two militaries, placing them on the verge of an open conflict.
Ukrainian politicians were set to consider a presidential request for the introduction of martial law in the country later on Monday.
The Ukrainian navy said six of its seamen were wounded when Russian coast guards opened fire late on Sunday on three Ukrainian ships near the Kerch Strait and then seized them.
Russia said three Ukrainian sailors were lightly injured and given medical assistance.
Ukraine's president, Petro Poroshenko, chaired an emergency meeting of his cabinet early on Monday and asked parliament to introduce martial law 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."
Martial law could entail a variety of measures including closing the borders, imposing restrictions on foreigners entering the country, a ban on gun sales, a ban of any political gatherings and rallies and even closing down media outlets if they are deemed a threat to national security.
An emergency meeting of the United Nations Security Council was also called for Monday, while the EU and Nato called for restraint from both sides.
Mr Poroshenko had a phone call with Nato secretary-general Jens Stoltenberg to discuss the situation, and Nato later said that, at Mr Poroshenko's request, its ambassadors and Ukraine's envoy will hold emergency talks in Brussels later.
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".
EU chief Donald Tusk called on Russia to stop provoking Ukraine and urged the authorities to return any Ukrainian ships or sailors it is holding.
The European Council president tweeted: "I condemn Russian use of force in Azov Sea", and added that "Russian authorities must return Ukrainian sailors, vessels and refrain from further provocations".
He said he has discussed developments with Mr Poroshenko and will meet the Ukrainian leader's representatives later.
Mr Tusk added: "Europe will stay united in support of Ukraine."
Mr Poroshenko said at a meeting of Ukraine's national security council 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, which further escalated tensions that have soared since Russia annexed Ukraine's Crimean Peninsula in 2014 and backed a separatist insurgency in eastern Ukraine.
Ukraine said its vessels were heading to the Sea of Azov in line with international maritime rules, while Russia claimed 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 is spanned by a 19-kilometre (11.8-mile) bridge that Russia completed this year.
"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 Mr 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 December 30 with the vote in March.
Some politicians hit out at Mr Poroshenko's move as an attempt to influence the vote.
Polls show Mr Poroshenko trailing far behind 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, Dmitry Peskov, said that Mr 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 at a protest in the snowy streets outside the Ukrainian parliament.
They brandished yellow-and-blue flags with the Ukrainian national symbol, the trident, and a huge white banner reading "Don't back down!"