Russia and Ukraine forces have engaged in a maritime confrontation, reflecting rising tensions between Moscow and Kiev in the Black Sea near Crimea.

Three Ukrainian Navy ships circumnavigating Crimea en route to a Ukrainian port crossed into Russian territorial waters, the press service of the FSB's Crimean border department said on Monday as cited by RT.

"This morning at around 07.00 Moscow time, three ships of the Naval Forces of Ukraine, in violation of Articles 19 and 21 of the United Nations Convention of Sea Law, defining the coastal state's right to ensure safety in maritime space, crossed the Russian state border, unlawfully entering the off-limits water area of Russian sea territory," the FSB said in a statement.

However, Ukraine's navy claimed that Russia's border guards rammed one of its tugboats in the Black Sea off Crimea on Sunday in "openly aggressive actions."

Ukraine said the incident took place as three of its ships including two small warships were heading for the port of Mariupol in the Sea of Azov, an area of heightened tensions between the countries.

Meanwhile, the Russian Federal Security Service's border control department announced that it is making efforts to de-escalate the tension caused by the transgression of the three Ukrainian ships.

Moscow has clarified that Russia reserves the right to defend the waters east of Crimea as an integral part of its territory. The Black Sea peninsula in southern Europe rejoined Russia in 2014.

The reunion of Crimea has been a sticking point in the relations between the two countries.

Both Moscow and Kiev accuse each other of harassing each other's shipping in the area.

Last month, Russian President Vladimir Putin signed a decree allowing punitive measures against Ukraine.

In June 2018, Ukrainian President Petro Poroshenko signed a decree to expand sanctions on Russian companies and entities. The sanctions would last at least three years and included penalties on Russian lawmakers and top officials.

Washington and its Western allies have also imposed several rounds of sanctions against Russia both over the Crimean unification and an armed conflict that erupted in eastern Ukraine when Kiev launched military operations to quell pro-Russia protests there.