Russia said on Tuesday it hopes its ties with the EU had not yet crossed the point of no return over the Ukraine crisis after Brussels slapped more sanctions against Kremlin-backed separatists.

"We are hoping that the 'point of no return' has not yet been crossed," Russian Foreign Minister Sergei Lavrov was quoted as saying by the state news agency TASS at a meeting in the Belarussian capital Minsk.

The EU must speak with one voice to Russia over Ukraine and be ready to send a "clear message" it will impose more sanctions if necessary, Ukrainian Foreign Minister Pavlo Klimkin told AFP in an interview Monday.

"Now it is time to have a clear message to Moscow that further destabilization in Ukraine will trigger further steps by the EU," Klimkin said as he visited Brussels for talks with new EU foreign affairs chief Federica Mogherini.

President Vladimir Putin stuck to his guns as he refused to say where Moscow-backed Ukrainian separatists receive heavy arms from and said that people fighting a just cause "will always get weapons".

"Where did they get the armoured vehicles and the artillery systems?" Putin said in reply to a question from German TV network ARD in an interview broadcast Sunday.

Russia expelled several Polish diplomats for spying on Monday, deepening the worst East-West crisis since the Cold War as the EU eyed fresh sanctions against Moscow over the violence in Ukraine.

Fresh bloodshed in Ukraine between pro-Kremlin rebels and Kiev's forces added to the tensions after Russian President Vladimir Putin left a G20 summit in Brisbane early amid criticism from western leaders.

Ukrainian President Petro Poroshenko claimed his country was "prepared for total war" as fighting continued Sunday around the rebel stronghold of Donetsk.

After a week in which Kiev said several unmarked armored convoys of troops crossed the Russian border to reinforce rebels in the east, Poroshenko toughened his rhetoric, telling the German daily Bild: "I am not afraid of a war with Russian troops."

Workers on Sunday began removing the wreckage of Malaysia Airlines flight MH17 from rebel-held territory in eastern Ukraine, four months after it was shot down killing 298 passengers and crew.

Dutch experts supervised a crew from the emergency ministry of the self-proclaimed Donetsk People's Republic as they began cutting pieces of the plane's wreckage with metal saws at the crash site near the village of Grabove, an Agence France Presse reporter at the scene said.

French President Francois Hollande said Sunday he would not be pressured into delivering two warships to Russia, after delaying their handover due to the Ukraine crisis.

Sanctions-hit Russia risks deeper isolation from the global community unless it takes a different path on Ukraine, U.S. President Barack Obama said Sunday at the end of a stormy G20 summit.

Obama said if President Vladimir Putin "continues down the path that he is on, violating international law, providing heavy arms to the separatists in Ukraine.... then the isolation that Russia is currently experiencing will continue".

Russian President Vladimir Putin on Sunday shrugged off a hail of Western fire over the Ukraine crisis as G20 leaders wrapped up an annual summit focused on a drive to overhaul the global economy. 

At the summit in Brisbane, Putin broke protocol by delivering remarks to the media before the host leader's closing news conference, and then flew out a little early. 

Ukraine's President Petro Poroshenko issued a decree Saturday ordering the withdrawal of all state services from rebel-held eastern regions, a further acknowledgement that the Kremlin-backed statelets are effectively breaking away.

The latest move towards splintering the war-torn ex-Soviet country came after fresh clashes between government troops and rebel fighters claimed at least five civilian lives, including those of two children, despite a nominal ceasefire that has failed to end the bloodshed.