Allies of murdered Russian opposition leader Boris Nemtsov on Tuesday unveiled a report he worked on claiming that hundreds of Russian soldiers have been killed fighting in Ukraine.

The report -- based on media articles and information from families of Russian soldiers allegedly killed in Ukraine -- repeats widespread allegations of Russian military involvement in Ukraine that Moscow has consistently denied.

Chinese state-run media lauded Beijing and Moscow's increasing closeness Tuesday, dismissing Western suspicion over the relationship as the two countries began their first joint naval exercises in European waters.

The drills, involving nine Russian and Chinese warships and set to last 11 days, were launched at a Russian naval base near the Black Sea port of Novorossiysk, Moscow's defence ministry said late Monday.

U.N. Secretary-General Ban Ki-moon held a brief meeting in Moscow at the weekend with North Korea's parliament president Kim Yong-Nam, a U.N. spokesman said Monday.

Ban attended World War II commemorations in Moscow as did Kim who traveled to Russia after leader Kim Jong-Un cancelled a much-anticipated visit. 

Russia and pro-Moscow rebels in eastern Ukraine now have the capacity to launch new attacks "with very little warning" after a sustained military build-up, NATO head Jens Stoltenberg said Monday.

"In eastern Ukraine, Russia and the separatists (now) have capabilities which enable them to launch new attacks with very little warning time", violating a ceasefire agreed in February, Stoltenberg said.

President Vladimir Putin is expected Tuesday to host U.S. Secretary of State John Kerry for crucial talks in Sochi amid tensions over Ukraine, during the top U.S. diplomat's first visit to Russia since the start of the crisis.

Ties between Moscow and Washington collapsed after Russia seized Crimea and buttressed separatists in eastern Ukraine but after a year of raging tensions signs are emerging that both Russia and the West may be ready to seek detente.

Head of al-Mustaqbal Movement and former Prime Minister Saad Hariri will head to Moscow for a two-day official visit this week to tackle the crisis gripping Lebanon, at forefront the presidential vacuum.

Local newspapers reported on Monday that Hariri will meet during his visit to Russia President Vladimir Putin, Foreign Minister Sergei Lavrov and other senior officials.

Russian President Vladimir Putin on Sunday defended the infamous pact between Nazi Germany and the Soviet Union that agreed to divide up eastern Europe during a visit by German Chancellor Angela Merkel.

On August 23, 1939, Germany and the Soviet Union agreed to carve up eastern Europe between them in a secret clause of the Molotov-Ribbentrop Pact on non-aggression.

German Chancellor Angela Merkel on Sunday said there was still no genuine ceasefire in eastern Ukraine, as she paid a visit to Moscow to commemorate millions of Soviet soldiers and civilians who died in WWII.

"Unfortunately we still do not have a ceasefire today," Merkel said after talks with Russian President Vladimir Putin. 

German Chancellor Angela Merkel on Sunday paid tribute to Soviet soldiers killed in WWII as she called for cooperation with Russia amid tensions over Ukraine.

Merkel flew to Moscow to lay a wreath at the grave of the Unknown Soldier near the Kremlin walls, in an apparent compromise gesture after she skipped Russia's main festivities on Saturday.

South Korea said Sunday its envoy attending Russia's World War II anniversary ceremony briefly met North Korea's ceremonial head of state, a rare high-level encounter between the rival states.

Senior lawmaker Yoon Sang-Hyun, who was representing South Korean President Park Geun-Hye at the Moscow event, met the North's Kim Yong-Nam on Saturday, Seoul's foreign ministry said.