German Chancellor Angela Merkel has put the blame for the recent naval confrontation between Ukraine and Russia off Crimea squarely on Moscow.
She said it was “entirely the doing” of Russian President Vladimir Putin, and promised to raise the issue with him.
On Sunday Russia fired on Ukrainian ships sailing towards the Sea of Azov – which is shared between the two countries – and seized their crews.
Ukrainian leader Petro Poroshenko has urged Nato to send ships to the area.
President Putin accused him of creating the naval “provocation” to boost his ratings ahead of Ukraine’s 2019 elections.
President Poroshenko has implemented martial law across Ukraine’s border regions for 30 days in response to the crisis.
On Thursday he announced that Russians living in Ukraine would soon face restrictions on bank withdrawals, changing foreign currency and travelling abroad.
What happened off Crimea?
The incident happened on Sunday, when two Ukrainian gunboats and a tug were sailing in the Black Sea towards the port of Mariupol in the Sea of Azov – which is shared between Russia and Ukraine.
As the vessels approached the Kerch Strait, they were confronted by FSB border guards who opened fire, wounding at least three sailors.
The Kerch Strait separates Russia from Crimea, a Ukrainian peninsula that was annexed by Russia in 2014.
Ukraine says Russia is deliberately blockading Mariupol and another Ukrainian port on the Sea of Azov, Berdyansk, preventing ships from getting through the Kerch Strait.
The 24 captured Ukrainian sailors have now been given two months in pre-trial detention by a court in Crimea.
What did Angela Merkel say?
Speaking alongside Ukrainian Prime Minister Volodymyr Groysman in Berlin on Thursday, the chancellor accused Russia of restricting access to the Sea of Azov by building a bridge over the Kerch Strait.
She said the latest crisis was “entirely the doing of the Russian president” and accused Moscow of violating a 2003 agreement guaranteeing free movement in the area.
“I want the Ukrainian soldiers released,” she said, adding that she would talk to Mr Putin at a forthcoming G20 meeting in Argentina.
“The Ukrainian side has asked us to act wisely. There is no military solution to these problems – we have to emphasise that,” Mrs Merkel said.
Would Nato help Ukraine?
The North Atlantic Treaty Organisation is the world’s most powerful regional defence alliance.
Ukraine is not a member, but it is a Nato partner country, meaning they co-operate on some political and security issues.
Mr Poroshenko told Germany’s Bild newspaper: “We hope that states within Nato are now ready to relocate naval ships to the Sea of Azov in order to assist Ukraine and provide security.”
A Nato spokeswoman would not comment directly on Mr Poroshenko’s request, but stressed that “since Russia’s illegal annexation of Crimea in 2014, Nato has substantially increased its presence in the Black Sea”.
Analysis by Jonathan Marcus, diplomatic and defence correspondent
The call for Nato to deploy warships to the Sea of Azov raises a variety of diplomatic and practical problems.
In strict legal terms, Russia and Ukraine share access to its waters under a 2003 treaty. This though specifically states that warships from third countries can only enter the Sea or make port visits there with the express permission of the other party.
Russia is hardly likely to give such permission. In practical terms it could easily block the Kerch Strait as it did earlier this week by placing a merchant vessel across the channel.
Nato in any case might see such a visit as more likely to inflame tensions.
It’s more likely that Nato might seek to boost its naval deployments to the Black Sea where its members – Bulgaria, Romania and Turkey – are uneasy about Russia’s more assertive behaviour.
Indeed the alliance says that its vessels have already spent some 120 days on patrol or exercises in the Black Sea this year, compared with 80 in 2017.
What is Russia’s argument?
Mr Putin called the sea clash “a provocation” organised by Ukraine’s authorities “in the run-up to the Ukrainian presidential election”.
Mr Poroshenko has low popularity ratings. Recent polls suggest that only about 10% of the electorate plans to vote for him next year, with nearly 50% saying they would not vote for him under any circumstances, the Kyiv Post newspaper reported.
Mr Putin added that Mr Poroshenko’s decision to impose martial law after a mere “border incident” was extreme, because it was not even imposed during the conflict with pro-Russian separatists in eastern Ukraine in 2014.
Russian state media report that Moscow has delivered a battalion of S-400 surface-to-air missiles to north Crimea, and also plans to build a new missile early-warning radar station there.
Mr Putin insisted that Russia’s military response was appropriate as the Ukrainians had “trespassed” into Russia’s territorial waters.
However, Ukrainian officials published a map on Wednesday, placing all three Ukrainian boats just outside Crimea’s territorial waters at the time they were seized.