Russia-Ukraine updates: US to ban Russian carriers from its airspace

At least three Ukrainian border guards were killed near the southern port city of Skadovsk on Thursday morning after a commandant's headquarters was shelled by a Russian helicopter, according to Ukraine’s State Border Guard Service.

They are the first reported deaths after Russia launched military operations in Ukraine early Thursday.

An unknown number of personnel were also wounded, Ukraine’s State Border Guard Service said in a statement on its official Facebook page, noting that the border guards in the area were still fighting.

-ABC News' Julia Drozd

Leaders of the European Union are urging Russia to "immediately cease" its attack on Ukraine, saying "such use of force and coercion has no place in the 21st century."

"We condemn in the strongest possible terms Russia's unprecedented military aggression against Ukraine," European Council President Charles Michel and European Commission President Ursula von der Leyen said in a joint statement Thursday. "By its unprovoked and unjustified military actions, Russia is grossly violating international law and undermining European and global security and stability. We call on Russia to immediately cease the hostilities, withdraw its military from Ukraine and fully respect Ukraine's territorial integrity, sovereignty and independence."

They noted that EU leaders will meet later Thursday "to discuss the crisis and further restrictive measures that will impose massive and severe consequences on Russia for its action." They said von der Leyen "will outline a further sanctions package being finalized by the European Commission and which the Council will swiftly adopt."

In on-camera statements Thursday, the EU's top diplomat, Josep Borrell, pledged to "adopt a stronger package, the harshest package of sanctions we have ever implemented."

Von der Leyen added that the EU "will not let President Putin tear down the security architecture that has given Europe peace and stability over the past decades."

"Ukraine will prevail," she said.

-ABC News' Anastasia Bagaeva, Ines de la Cuetara and Aicha El Hammar Castano

Russia-backed separatists in eastern Ukraine's Donbas region claimed Thursday that their forces are taking over Ukrainian government-controlled territories amid a Russian invasion.

Ivan Filiponenko, a representative of the military department of the self-proclaimed Luhansk People's Republic, said in a statement that militia units have begun "artillery preparation and an operation to liberate the temporarily occupied territories."

Meanwhile, Eduard Basurin, a spokesman for the militia of the self-proclaimed Donetsk People's Republic, told Russia's Interfax news agency that "forces are delivering strikes on positions of the Ukrainian Armed Forces along the entire line of contact, using all weapons that are available to them."

Separatist leaders want to control all of the Luhansk and Donetsk regions in Donbas. But they currently only have about a third, with the rest controlled by Ukraine.

-ABC News' Tanya Stukalova

Russia claimed Thursday to have neutralized some of Ukraine's military infrastructure amid an attack on the country.

"The military infrastructure of air bases of Ukraine's Armed Forces has been rendered inoperable," the Russian Ministry of Defense said in a statement. "Air defense systems of the Ukrainian Armed Forces have been suppressed."

The Russian defense ministry further alleged that Ukrainian forces on the border "are offering no resistance to Russian units."

Meanwhile, a statement from the Ukrainian Ministry of Defense claimed that five Russian planes and a helicopter had been shot down.

"Reports of foreign media on a Russian aircraft allegedly downed on the Ukrainian territory have nothing to do with the reality," the Russian defense ministry said Thursday.

ABC News could not independently verify the claims on either side.

-ABC News' Tanya Stukalova