The Security Service of Ukraine (SBU) detained a Russian tanker at the port of Izmail near Odesa on Thursday over confrontation in the Kerch Strait.
Late November 2018, Russia seized two Ukrainian navy ships and a navy tugboat along with 24 crew members for entering its waters in the Kerch Strait, provoking conflict.
The Russian tanker, Nika Spirit, was identified by the Ukrainian special service as tanker Nеyma, which allegedly blocked Ukrainian vessels in the Kerch Strait last year.
"The Security Service of Ukraine together with the Military Prosecutor's Office detained the Russian tanker Neyma, which had blocked the Ukrainian military ships in the Kerch Strait," the SBU said in a statement.
The seized tanker is considered a piece of evidence as the SBU is preparing a petition to the court for its arrest, the SBU added.
The Russian Foreign Ministry said the country's embassy is investigating the circumstances of the incident.
"If we are talking about taking Russians hostage, it will be qualified as a grave violation of international law, and then it will have its consequences soon," a ministry source told reporters in Moscow.
The source also added that the episode will not contribute to the release of the Ukrainian sailors who are currently in a pretrial detention center in Moscow.
Russia and Ukraine have been at loggerheads since 2014 when Russia annexed Crimea after a controversial referendum.
Turkey, as well as the UN General Assembly, viewed the annexation as illegal.
Ukraine also blamed Kremlin for separatist violence in eastern Ukraine, near the border with Russia.
The situation aggravated after the Malaysian Airlines Flight 17 was shot down over eastern Ukraine en route from Amsterdam to Kuala Lumpur, killing all 283 passengers and 15 crew members on board, including 28 Australians.
Kiev put the responsibility on the pro-Russian militants in Donbas. In turn, Moscow accuses Ukraine of shooting down the plane.
By Elena Teslova in Moscow