A court in Russian-annexed Crimea on Tuesday ordered three Ukrainian sailors to be held in custody for two months after a weekend confrontation at sea with Russian border guards.
"For now, the court has ordered three people held until January 25" on accusations of crossing into Russian territory illegally, Crimea's rights ombudswoman Lyudmila Lubina told AFP news agency at the court.
Several others of the more than 20 Ukrainian sailors held by Russia were expected to appear before the court later on Tuesday.
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 dangerous crisis between the ex-Soviet neighbours in years.
Kiev says 23 are in detention, while Russian officials have put the figure at 24.
Three of the Ukrainian sailors were wounded in the clashes and are being treated in a Crimean hospital.
Russia has sharply increased its military presence on the border with Ukraine, Ukrainiain President Petro Poroshenko said on television on Tuesday, warning of a threat of "full-scale war."
"The number of (Russian) tanks at bases located along our border has grown three times," Poroshenko said in an interview.
He said, "the number of units that have been deployed along our border –– what's more, along its full length –– has grown dramatically."
Viktor Yushchenko, Ukraine's ex-president, told TRT World that Russia is "a great threat" to Europe and "Europe has not been adequate in meeting the world's biggest challenge."
Russia resists calls to free sailors
Russia has so far resisted calls to release them, accusing the sailors of crossing illegally into Russian waters and of ignoring warnings from its border guards.
The incident was the first major confrontation at sea in the long-running conflict pitting Ukraine against Moscow and Russian-backed separatists in the country's east.
The court hearings took place in Simferopol, the main city in Russian-annexed Crimea, and are expected to continue on Wednesday.
TRT World speaks with Luke Coffey, former special advisor to UK Ministry of Defence.
Trump reconsiders Putin meeting
US President Donald Trump said on Tuesday he may cancel his scheduled meeting with Putin at the G20 summit in Argentina because of Russia's maritime clash with Ukraine.
In an interview with the Washington Post, Trump said he was awaiting a "full report" from his national security team Tuesday evening about Russia’s capture of three Ukrainian naval ships and their crews on Sunday.
"That will be very determinative," Trump told the Post. "Maybe I won't have the meeting. Maybe I won't even have the meeting ... I don't like that aggression. I don't want that aggression at all," he said.
Meanwhile, the US State Department said Europe needs to do more to enforce sanctions against Moscow.
EU to consider sanctions
The European Union will next month consider further sanctions against Russia over the latest flare-up in the Ukraine conflict, the foreign minister of Austria, which holds the rotating EU presidency, said on Tuesday.
"On the issue of further sanctions, time will tell – we have a summit in December," Karin Kneissl told reporters after Berlin talks with her German counterpart Heiko Maas.
"Everything depends on the accounts of events and the actions of both sides. But it will need to be reviewed."
TRT World spoke to Professor Alexander Domrin, of the National Research University Higher School of Economics for his insight into the Russia-Ukraine tensions.
Kneissl said it was "one side's account versus the other's" in the latest tensions, in which Kiev declared martial law in response to Moscow's seizure of three of its navy vessels.
Maas said the latest escalation showed "that the annexation of Crimea ... is also a problem for the security of us all in Europe."
The United States and EU have already imposed sanctions on Russia over the Ukraine conflict.
Ukraine's Western allies have accused Russia of using force without justification in the naval confrontation, while Kiev urged its partners to impose further sanctions on Moscow.
The next meeting of EU foreign ministers is scheduled for December.
Any further sanctions would have to be agreed unanimously by the EU, which would be tricky given the divisions between members in their stance toward Moscow.
Italian Deputy Prime Minister Matteo Salvini, in particular, has opposed economic sanctions against Moscow and advocated dialogue.
UN calls for 'restraint'
Ukraine and Russia must exercise "maximum restraint," UN chief Antonio Guterres said on Tuesday, appealing for a quick reduction in tensions after a naval confrontation sparked the most dangerous crisis in years between the neighbours.
His call came as Russian President Vladimir Putin warned Ukraine against any "reckless acts" after Kiev declared martial law in response to Moscow's seizure of three of its navy vessels.
A statement from the UN secretary general urged both sides "to take steps without delay to contain this incident and reduce tensions through all available peaceful means in accordance with the Charter of the United Nations."