New unidentified armored columns rumbled toward the pro-Moscow rebel stronghold in eastern Ukraine on Monday as fears grew of a return to all-out fighting in the war-torn region.

The Netherlands meanwhile was set to hold an emotional ceremony for the victims of the MH17 flight shot down over the separatist-held eastern Ukraine in July in a tragedy that brought the conflict in the ex-Soviet state to the international fore.

The leaders of China and Japan held an ice-breaking summit Monday after two years of dangerous animosity, as world leaders including Barack Obama gathered for an Asia-Pacific meeting spotlighting intensifying big-power rivalries.

Xi Jinping and Shinzo Abe met in Beijing's Great Hall of the People in what the Japanese prime minister said was a "first step" towards repairing the fractured relationship between the world's second- and third-largest economies.

Chinese President Xi Jinping and his Russian counterpart Vladimir Putin promised ever closer cooperation Sunday as they met for the 10th time in less than two years.

The two men, who held talks in Beijing, have increasingly stressed their shared outlooks which mirror their countries' converging trade, investment and geopolitical interests.

Armored convoys headed to bolster rebel positions in east Ukraine Sunday as shelling rocked separatist stronghold Donetsk and fears mounted of a return to full-scale fighting.

Shelling rumbled on throughout the afternoon on the edge of Donetsk, where government forces regularly exchange heavy fire with insurgent fighters, but was less intense than overnight when mortar fire was heard close to the center for around two hours, an AFP journalist reported.

Germany marks 25 years since the euphoric fall of the Berlin Wall Sunday with more than a million people expected to join tributes, festivities and an open-air party with freedom icons and rock stars.

Chancellor Angela Merkel leads commemorations for those killed trying to flee communist East Germany, ahead of a giant festival to celebrate the peaceful revolution that ended Europe's Cold War division on November 9, 1989.

The Soviet Union's last leader Mikhail Gorbachev warned Saturday that the world was on the "brink of a new Cold War" at an event to mark 25 years since the Berlin Wall's fall, the German news agency DPA reported.

"The world is on the brink of a new Cold War. Some are even saying that it has already begun," the 83-year-old said, amid tensions between the West and Russia over Ukraine.

The last remains of the victims from downed Malaysia Airlines flight MH17 might never be fully recovered, the Dutch foreign minister said Saturday, as five more coffins were flown out of Ukraine. 

"We cannot say at this moment in any certain way at what moment and even if we can recover the last nine (victims), but we will do everything we can in cooperation with authorities here to make that happen and that work is still possible to do," Foreign Minister Bert Koenders told journalists after a ceremony at Kharkiv airport.

Russia's top diplomat Sergei Lavrov said Saturday that U.S. involvement in resolving the conflict in Ukraine would be a "step in the right direction", after meeting with his U.S. counterpart John Kerry in Beijing.

Lavrov's remarks appeared to soften Russia's line on the crisis ahead of high-level meetings between President Vladimir Putin and world leaders at an APEC summit in China and a Group of 20 summit in Australia next week.

Progressive Socialist Party leader MP Walid Jumblat held talks in the Russian capital Moscow with former Syrian National Coalition leader Ahmed Moaz al-Khatib.

According to al-Akhbar newspaper published on Saturday, the meeting between Jumblat and Khatib was held at the headquarters of the Russian Foreign Ministry.

Australian Prime Minister Tony Abbott said Saturday he would have a "robust" conversation about downed Malaysia Airlines Flight MH17 with Russian President Vladimir Putin when they meet in Beijing. 

The Kremlin confirmed on Friday that Putin will meet Abbott, who last month promised to confront the Russian president over the downing of the plane, at a summit in the Chinese capital.