Ukraine announced it was barring entry to Russian men between 16-60 years and a senior state security official said Kiev was considering whether to respond in kind with "mirror actions" to the Black Sea incident.
Earlier, in a move applauded in Kiev, U.S. President Donald Trump called off a meeting with Russia's Vladimir Putin in Argentina to signal Washington's disapproval of Russian behaviour in the naval clash with Ukraine.
The Russian rouble, which is sensitive to events that might lead to new sanctions being imposed on Russia, fell on news of the cancelled meeting. Moscow said it expected the leaders to have an impromptu meet.
In a further boost to Ukraine, the EU released 500 million euros in financial assistance to Kiev and European Council President Donald Tusk predicted Brussels would roll over sanctions on Russia at a summit on Dec. 13-14.
President Petro Poroshenko, referring to Russia's seizure and subsequent annexation of Crimea in 2014 and its support for separatist uprisings in eastern Ukraine, said banning Russian men was important for stopping a full-scale invasion.
"These are measures to block the Russian Federation from forming detachments of private armies here, which in fact are representatives of the Armed Forces of the Russian Federation," Poroshenko said.
"And not allow them to carry out the operations that they tried to conduct in 2014," he added.
The EU has propped up Ukraine's war-scarred economy since the Crimea annexation while prodding the pro-Western authorities to pass reforms and tackle corruption.
"Today's European Commission decision on disbursement comes at a crucial moment when Ukraine and its people face a new aggression from Russia and need to see solidarity from international partners," said Commission Vice President Valdis Dombrovskis.
The G7 group of nations also weighed in on Ukraine's behalf, blaming Moscow's actions that had "dangerously raised tensions."
Ukraine and Russia have blamed each other for last Sunday's clash at the Kerch Strait through which ships have to pass to reach Ukrainian ports at Berdyansk and Mariupol.
Russia has moved the 24 sailors it captured to prisons in Moscow, where three of them are being treated in a prison hospital, Russian TV said. Foreign Minister Pavlo Klimkin said Ukraine was trying to get consular access to them.
Sunday's clash prompted Ukraine to introduce martial law for a period of 30 days from Wednesday in regions of the country thought most vulnerable to a Russian attack.
A senior ally of German Chancellor Angela Merkel said the EU and United States should consider banning from their ports Russian ships originating from the Azov Sea as a tit-for-tat measure.
Russia says it will deploy a new division of Pantsir medium-range surface-to-air systems - comprising between 12 and 18 military vehicles - on the Crimean peninsula by the end of the year, Interfax news agency quoted a spokesman for the Southern Military District as saying.
The planned deployment comes after Russia announced it had deployed a new battalion of advanced S-400 surface-to-air missile systems, its fourth such battalion, to the peninsula's north. A Crimean security source was also quoted by Interfax on Thursday saying that Russia planned to build a new missile early-warning radar station in Crimea next year.
Russian officials accuse Poroshenko of artificially manufacturing a crisis to prop up sagging ratings ahead of an election next March.
But the incident has prompted renewed calls for more Western sanctions on Russia.
Tusk will chair an EU summit on Dec. 13-14, which is due to roll over for another year the bloc's measures against Russia's defence, energy and banking sectors.
"Europe is united in its support to Ukraine's sovereignty and territorial integrity. This is why I am sure that the EU will roll over the sanctions against Russia in December," Tusk told a news conference in Argentina.
The United States and the EU have imposed sanctions on Russia since 2014, when Moscow annexed Crimea after a pro-Russian leader was toppled in Kiev.
Fighting between Ukraine and Moscow-backed separatists has killed more than 10,000 people. Major fighting ended with a 2015 ceasefire but deadly exchanges of fire are still frequent. (Additional reporting by Natalia Zinets and Olena Vasina in Kiev, Katya Golubkova and Maria Tsvetkova in Moscow, Alastair Macdonald and Gabriela Baczynska in Brussels, Andreas Rinke and Paul Carrel in Berlin; Writing by Matthias Williams; Editing by Richard Balmforth)
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)