Ukraine said Tuesday that the leaders of Germany and France had agreed to back "firm" steps against Russia should pro-Moscow rebels hold disputed elections in the ex-Soviet state's separatist east.

A top aide to President Petro Poroshenko said German Chancellor Angela Merkel and French President Francois Hollande had agreed at trilateral talks in Berlin on Monday to a set of "red lines" Russia must not cross.

A Russian military court on Tuesday sentenced a Ukrainian filmmaker to 20 years in a strict-regime prison colony on terror charges in a trial condemned by Kiev, Western rights groups and top film directors.

Oleg Sentsov, 39, was convicted for allegedly carrying out arson attacks on pro-Kremlin party offices in Crimea after it was seized by Russia last March, and plotting further attacks, including blowing up a Lenin statue in the peninsula's main city of Simferopol.

Ukraine and pro-Russian rebels on Tuesday reported the deaths of five people in clashes in the east that raged despite a new EU push to end one of Europe's bloodiest conflicts in decades.

A spokesman for the army in Kiev said four servicemen were killed and 12 injured in mortar fire exchanges across the eastern separatist province of Donetsk.

The United States soon will deploy F-22 Raptors in Europe, sending the stealth fighter jets to reassure NATO partners concerned about Russia's actions in Ukraine, a Pentagon official said Monday.

Air Force Secretary Deborah Lee James did not offer specifics about where or when the single-seat jets would be deployed, citing operational security reasons. James also would not say how many of the planes would be deployed.

Ukrainian President Petro Poroshenko on Monday accused Russia of sending major military backup to pro-Moscow rebels, speaking just ahead of talks on the conflict with German Chancellor Angela Merkel and French President Francois Hollande.

"Just this week three big convoys crossed our border towards Lugansk, Donetsk and Debaltseve," Poroshenko said, referring to rebel-controlled areas of eastern Ukraine.

Japanese Prime Minister Shinzo Abe on Monday criticized his Russian counterpart Dmitry Medvedev's weekend visit to disputed islands, aggravating a long-running dispute over the archipelago.

The visit "conflicts with Japan's position and hurts the feelings of the Japanese people. It is extremely regrettable," Abe told a parliamentary panel when asked about the trip.

Russian Prime Minister Dmitry Medvedev landed Saturday in the Kuril islands, prompting a swift rebuke from Tokyo, which claims sovereignty over the northwest Pacific archipelago in a long-running dispute.

Medvedev visited Iturup, one of four islands in the chain that lies off Russia's far eastern coast and just north of Japan, Russian media reports said.

Russia and China on Friday started joint military drills in the waters and airspace of the Sea of Japan, Russia's military said. 

The exercises off the Russian city of Vladivosktok -- which are set to run until August 28 -- will involve 22 vessels, up to 20 aircraft and over 500 marines from the two sides, the Russian armed forces said in a statement. 

European Commission chief Jean Claude Juncker will hold talks in Brussels next week with Ukrainian President Petro Poroshenko about the tattered ceasefire in eastern Ukraine, the EU said Friday.

Juncker will meet with Poroshenko next Thursday to discuss "implementation of the Minsk agreement," Commission spokeswoman Annika Breidthardt told reporters.

A Russian court on Friday turned down an appeal to shift the high-profile trial of a Ukrainian female helicopter pilot from southern Russia to Moscow, her lawyer said. 

Nadiya Savchenko, 34, went on trial last month in a provincial court close to the Ukrainian border for her alleged involvement in the killing of two Russian journalists in war-torn eastern Ukraine last year.