Russia seized three Ukrainian naval ships and took their crew prisoner at the weekend, prompting Ukraine's President Petro Poroshenko to say there was now an "extremely serious" threat of a Russian land invasion. Six Ukrainians were injured.
His comments came two days after Russian forces seized three Ukrainian ships and their crews in the Black Sea.
U.S. Secretary of State Mike Pompeo called the Russian seizure of the Ukrainian ships "a risky escalation and a violation of worldwide law".
Outgoing U.S. Ambassador to the United Nations Nikki Haley retweeted Peterson and added, "An emergency Security Council meeting has been called for tomorrow [Monday] at 11:00am". "As stated in our Crimea Declaration, the United States rejects Russia's attempted annexation of Crimea".More news: Melania Trump uses Christmas decorations to promote 'Be Best' campaign
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The approved measures included a partial mobilization and strengthening of air defenses.
But Poroshenko insisted it was necessary because what happened in the Kerch Strait between Crimea and the Russian mainland "was no accident", adding that "this was not the culmination of it yet".
They have been held by Moscow since Sunday, after Russian forces captured three of Kiev's ships off the coast of Crimea, sparking the most unsafe crisis between the ex-Soviet neighbours in years.
One of them appeared to be reading from a teleprompter, prompting suggestions from Kiev that they were forced to confess under duress. Ukrainian authorities said they had given advance notice to Russian Federation that the boats would be moving through the strait.More news: Winter storm causing travel problems in southern Iowa
NATO Secretary-General Jens Stoltenberg said Poroshenko assured him that martial law would not have a negative impact on the election. "We will remain in contact with the Ukrainian government to underline our support".
Russian state media has reported the confrontation is a provocation orchestrated by Ukraine and others in America to disrupt the forthcoming meeting between Russian President Vladimir Putin and President Donald Trump at the G20 summit in Buenos Aires this week.
"Either way, we don't like what's happening".
"I know those sailors from Nikopol". They´re working on it too.
"It's not a political issue here, because we can have an argument about the legal status, but it's about simply concentrating on protecting them and helping them", Foreign Minister Pavlo Klimkin told the AP. She also warned that any further escalation by the Kremlin will "further sour Russia's relations with the USA and many other countries".
Earlier, the Russian envoy to the United Nations, Dmitriy Polyanskiy, said at a November 26 UN Security Council emergency session in NY that two SBU officers had been on board one of the Ukrainian military vessels trying to enter the Sea of Azov through the Russian-controlled Kerch Strait. The Security Council then discussed the clash under terms laid out by Ukraine. It is the only outlet to the Black Sea from the Sea of Azov, location of major Ukrainian ports. There is also dispute between the two countries over whether Ukraine notified Russia in advance about the ships passing through the strait, with Moscow denying Kiev's statement that its military alerted the Russian forces multiple times of its intentions.More news: Jerome Corsi: rightwing author pursuing plea deal with Robert Mueller
In a speech on Tuesday, German Foreign Minister Heiko Maas said Moscow must respect worldwide law and territorial sovereignty.