Australian Treasurer Joe Hockey confirmed Sunday Vladimir Putin will attend the G20 leaders' summit in November, despite concerns about Russia's actions in Ukraine in recent months.

Australia's confirmation that the Russian leader would attend the high-powered summit came after Ukraine's President Petro Poroshenko said he would also meet Putin next week.

Ukraine's President Petro Poroshenko on Saturday said he will meet with Russia's Vladimir Putin next week as Kiev reported rebel attacks have subsided, signaling the possibility of rescuing a truce in the six-month conflict.

Pro-Russian rebels and the Ukrainian military in the eastern Donetsk region said they have agreed to a no-shooting period, and the army announced "progress" in negotiations and readiness to pull back forces.

Former Soviet leader Mikhail Gorbachev was on Friday discharged from a Moscow clinic where he had been admitted for medical tests.

"I am feeling better today than I was yesterday. That is why doctors agreed that it was possible to allow me to leave the clinic," Gorbachev, 83, told the Interfax news agency.

Russian President Vladimir Putin marked his 62nd birthday roaming the Siberian wilderness on Tuesday, as supporters compared his takeover of Crimea to a Herculean labor and 100,000 marched in Chechnya in his honor.

Kremlin spokesman Dmitry Peskov said Putin had taken a day off from his "extremely intense" schedule to celebrate his birthday in the depths of Siberia.

Bulgarian President Rosen Plevneliev denounced Russia's Vladimir Putin as an aggressive leader with a 19th-century empire-building style, in comments to be published Saturday.

"Russia is a nationalistic and aggressive state," Plevneliev told Germany's Frankfurter Allgemeine Zeitung.

Pro-Russian insurgents launched a fresh assault Thursday on an airport held by isolated Ukrainian forces as a month-old truce came under renewed strain and calls grew for the Kremlin to help halt the bloody revolt.

Ukraine also dispatched its energy chiefs to Brussels in a bid to convince the European Union to back up Kiev at crunch talks with Russia on the latest energy war with its westward-leaning but effectively bankrupt neighbor.

The European Union said Friday that Russian President Vladimir Putin had written to Brussels demanding changes to a landmark EU-Ukraine accord, but it ruled out reopening the deal without Kiev's consent.

Putin's letter to European Commission chief Jose Manuel Barroso reportedly threatened retaliatory measures if the EU and Ukraine do not stick to their agreement with Moscow to delay the implementation of the deal until 2016.

Japan hit Russia with further sanctions on Wednesday over the crisis in Ukraine, in a further blow to efforts to end a longstanding territorial row between the pair.

The fresh penalties, targeting exports of military equipment and technology to Russia, come a day after Japanese Prime Minister Shinzo Abe reportedly dropped plans to host President Vladimir Putin later this year due to tensions over the conflict.

Prime Minister Shinzo Abe has dropped plans to host Russian President Vladimir Putin in Japan this year due to friction after Tokyo imposed sanctions on Moscow over the Ukraine crisis, reports said Tuesday.

The two countries had agreed on the Russian leader's visit "this autumn" but Washington had asked Tokyo to postpone it, Kyodo News reported, quoting Japanese government sources.

Russian President Vladimir Putin and Japanese Prime Minster Shinzo Abe held telephone talks Sunday amid speculation about whether a visit by Putin will go ahead due to frictions over Ukraine.

Local media reports say Putin's visit to Japan planned for this autumn is now uncertain following Tokyo's sanctions on Moscow over the crisis in Ukraine.