The United States says it will provide an additional $10 million in military aid to Ukraine to boost its naval capability, after Russia seized three Ukrainian navy ships off the coast of Crimea last month.

The State Department announced the decision on Friday, urging Moscow to “immediately return to Ukraine the seized vessels and detained Ukrainian crews.”

Last month, Russian naval forces seized two Ukrainian armored artillery vessels and a tug boat, saying they had illegally entered its territorial waters.

The flotilla, it said, had not notified Russia of its plans in advance and ignored warnings to stop while maneuvering dangerously. 

The State Department called on Russia “to keep the Kerch Strait and the Sea of Azov open to ships transiting to and from Ukrainian ports, and to respect Ukraine’s sovereignty and territorial integrity.”

The Sea of Azov is a strategic ocean route linked to the Black Sea by the narrow Strait of Kerch where Russia has built a bridge to link the Crimean Peninsula with the mainland.

Tensions escalated earlier this year after Ukraine detained two Russian ships for port calls on Crimea, which rejoined Russia in a 2014 referendum.

The move prompted Russia to increase patrols off its Azov coast to guarantee free navigation by Russian ships.

Following the November incident, the European Union said tensions in the Azov Sea and Kerch Strait had "increased dangerously," and that Russia must restore freedom of passage.

EU extends sanctions against Russia

The European Council said on Friday that the bloc formally agreed to extend its economic sanctions against Moscow by six more months.

The council said it had adopted its decision on the extension of sanctions unanimously.

The measures, focused on financial, energy and defense sectors, as well as dual-use goods, will last until July 2019.

The sanctions were initially imposed in July 2014 after Crimea rejoined Russia. The West, which brands the reunification as annexation of the Crimean territory, accuses Moscow of having a hand in the conflict in eastern Ukraine, a charge Russia denies.

‘UK ship in Ukraine to send message to Russia’

Amid the simmering tensions between Russia and Ukraine, British Defense Secretary Gavin Williamson said they have sent a Royal Navy ship to the Black sea in support of Kiev and that the Black Sea did not belong to Russia.

Williamson, who was in a visit to Kiev on Friday, said the navy ship, HMS Echo, which has docked at the port of Odessa earlier this week, was sending a strong message to Moscow.

“What we are saying to Russia, what we are saying to President Putin – they cannot continue to act with no regard or care for international laws or international norms," he said.

Russia says the Royal Navy vessel is used to collect data about the ocean, calling it a spy ship.

Russia expels Swedish diplomat

Russia on Friday called on a Swedish diplomat to leave the country after the government in Stockholm denied diplomatic visa to two Russian diplomats, according to the Swedish foreign ministry.

“The Swedish Foreign Ministry announced it had refused to satisfy Russian applications for diplomatic visas. And Russia responded to this by asking a diplomat at the Swedish Embassy in Moscow to leave the country,” said a press officer.

Swedish newspaper Expressen wrote that Stockholm has denied visas to the Russian diplomats over concerns that they may have links to the Russian intelligence services.

Sweden had previously accused Russia of using fake news, false documents and disinformation as part of a coordinated campaign to influence public opinion and decision-making in the country. Moscow has denied the allegations.