Russia on Friday insisted that Ukrainian sailors it captured after seizing their vessels will go on trial for violating its maritime borders, despite international calls for their release.
Russian Foreign Minister Sergei Lavrov said the 24 Ukrainian sailors currently in pre-trial detention will be put in the dock for violations of Russian and international law.
"When the investigation is over, there will be a trial," he told reporters after a meeting in Milan of the Organisation for Security and Co-operation in Europe (OSCE).
Russia's top diplomat suggested that after a trial verdict, measures could be taken to improve the sailors' situation, without specifying if they could be pardoned or released as part of an exchange with Kiev.
"As soon as the trial is over, we will have different possibilities in accordance with Russian legislation," he said.
"Then it will be possible to say how to make their lives easier or agree to some concrete steps. But this will be done only after the trial has been completed."
Last month Russia opened fire on three Ukrainian navy vessels as they tried to pass through the Kerch Strait from the Black Sea to the Sea of Azov.
The 24 Ukrainian crew members were detained.
Despite international calls for their release, the courts ordered the sailors to be held in pre-trial detention for two months and they are now in Moscow.
Three of them are undergoing treatment for injuries. The seamen face up to six years in prison for illegally crossing Russia's borders.
Critics of the Kremlin have warned Russia is preparing a show trial.
Ukrainian President Petro Poroshenko has insisted they are "prisoners of war" and should be immediately released. Ukraine has introduced martial law in border and coastal areas for 30 days following the incident.
The seamen have joined a long list of Ukrainians jailed in Russia including filmmaker Oleg Sentsov, who refused food for 145 days in an Arctic penal colony earlier this year.
The incident with the Ukrainian ships was the most dangerous in years between the ex-Soviet neighbours.
They have been locked in a confrontation since 2014 when Russia annexed Crimea and supported an insurgency in eastern Ukraine.
More than 10,000 people have been killed in the conflict.
Speaking to reporters, Lavrov also denounced what he said were Washington's plans to ditch the New START nuclear treaty, set to expire in 2021.
"There's an impression that the groundwork is being laid for the destruction of this document too," he said.
The two former Cold War enemies have recently clashed over the fate of another key arms-control treaty, the Intermediate-Range Nuclear Forces treaty (INF).
Lavrov also slammed Washington for the arrest of Huawei's chief financial officer, Meng Wanzhou, in Canada at the request of the United States, saying it sought to apply its laws outside its jurisdiction.
"These are very arrogant, super-power-like policies. Even the United States' closest allies already find them annoying," Lavrov said. "It's time to put an end to this."