UN Secretary-General Antonio Guterres on Tuesday urged restraint and a peaceful solution to an incident between Russian and Ukrainian vessels in the Black Sea.
"The Secretary-General urges both parties to exercise maximum restraint and to take steps without delay to contain this incident and reduce tensions through all available peaceful means," a spokesman for Guterres said in a statement.
Guterres stressed the "need to avoid any risk of further escalation of the situation."
"The sovereignty and territorial integrity of Ukraine, within its internationally recognized borders, in accordance with relevant General Assembly and Security Council resolutions, must also be fully respected," the statement added.
The Ukrainian navy on Sunday accused Russia of opening fire on its warships off Crimea, asserting that its crew members were wounded and its vessels were seized. Russia said the vessels had ignored calls to stop, sparking military action, as they were relocating from Odessa to the Port of Mariupol.
The Russian military seized the vessels and said three Ukrainian servicemen were wounded in the incident. However, Ukrainian officials say that six servicemen were injured.
Russia and Ukraine have been at loggerheads since 2014, when Russia annexed Crimea after a controversial referendum.
Ukraine has also blamed Russia for separatist violence in eastern Ukraine, near the border with Russia.