The Kremlin warned Tuesday that a simmering war in eastern Ukraine could boil over after Russia seized three Ukrainian ships and Kiev responded by declaring martial law in parts of the country. Russia paraded the captured seamen on television, a move that Ukraine called criminal.
Russia and Ukraine have blamed each other for Sunday’s confrontation in the Kerch Strait, which links the Black Sea and the Sea of Azov. The clash has raised the specter of renewing a full-blown conflict in eastern Ukraine and saw Russia strongly criticized at the United Nations by the United States and its allies.
The Ukrainian parliament on Monday adopted a motion by the president to impose martial law for 30 days. That is something Ukraine avoided doing even when Russia annexed its nearby Crimean peninsula in 2014 or sent in clandestine troops and weapons to insurgents in war-torn eastern Ukraine.
On Sunday near Crimea, Russian border guards rammed into and opened fire on three Ukrainian navy vessels traveling from the Black Sea toward a Ukrainian port. The Russians seized the ships and their crews.
Ukraine considers the 24 captured men to be prisoners of war and says some have been seriously injured, while Russia says they are individuals who have violated its border.
The Kremlin reacted strongly to Ukraine’s declaration of martial law, with Dmitry Peskov, Russian President Vladimir Putin’s spokesman, telling reporters Tuesday that it might trigger a flare-up in hostilities in eastern Ukraine.
Ukrainian troops have been fighting Russian-backed separatists in eastern Ukraine since 2014, a conflict that has left over 10,000 dead, but fighting has eased since a truce in 2015.
WATCH: Relatives of captured Ukrainian soldiers in the dark about their whereabouts, condition
The martial law formally went into effect on Monday in several parts of Ukraine, including areas bordering territory now held by the separatists.
The Russian intelligence agency FSB claimed the ships had Ukrainian SBU intelligence agents onboard with a mission to mount what they called “provocation” in the Kerch Strait.
The strait is spanned by a new bridge that Russia completed this year — the only land link from the Russian mainland to the annexed peninsula of Crimea.
The SBU on Tuesday confirmed it had officers on the ships but denied any nefarious intentions, saying they were simply fulfilling counterintelligence operations for the Ukrainian navy.
The SBU also demanded that Russia stop using “psychological and physical pressure” on the Ukrainians — an apparent reference to interviews of the crewmembers that Russia released late Monday. The video broadcast by Russian state television showed three separate interviews with Ukrainian seamen, all of whom agreed with Russian claims that they violated its border.
WATCH: Tensions escalate after Russia seizes Ukraine naval ships
It was not immediately possible to ascertain if the men were talking under duress or had been subject to violence. One of them was clearly reading from a script prepared for them.
Ukraine’s foreign minister told The Associated Press on Tuesday that he has asked the president of the International Committee of the Red Cross to arrange a visit to the Ukrainian prisoners and he’s waiting for a Russian response. He said some of the seamen on the seized ships had been seriously injured in the clash with Russia.
“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.
When asked about the Ukrainian seamen broadcasts on Russian TV, Klimkin said “even to put prisoners of war on television is already a crime.”
A court in Crimea on Tuesday ordered that one of the Ukrainians be kept in custody pending a trial. He could be sent to prison for six years if found guilty. Rulings for possible arrest of 11 more Ukrainian seamen are expected later in the day while the court will rule on the remaining 12 on Wednesday.
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 narrow Kerch Strait.
Putin and German Chancellor Angela Merkel spoke on the phone early Tuesday, and the Russian president expressed a “serious concern” about what the martial law in Ukraine might entail.
Meanwhile, German Foreign Minister Heiko Maas said Tuesday that Berlin has “called on Russia and Ukraine to show the greatest possible restraint” and suggested that Germany, France, Russia and Ukraine could work together to resolve the tensions.
WATCH: Freeland condemns Russian seizure of Ukrainian ships
Russian Foreign Minister Sergey Lavrov, who was visiting Paris on Tuesday, rejected that offer, saying that he did not see “a need for any kind of mediators.” He spoke after meeting with French Foreign Minister Jean-Yves Le Drian, who appeared to soften his criticism of Russia’s seizure of the ships.
Shortly after Russian border guards seized the Ukrainian ships off Crimea, France’s Foreign Ministry said “nothing justifies” Russia’s use of force.
But after long talks with Lavrov in Paris, Le Drian blamed the ship standoff on the “high level of militarization” in the region and avoided pointing the finger at Russia.
The United States and the European Union have slapped sanctions on Russian businesses, tycoons and banks for Russia’s 2014 annexation of Crimea.