Ukrainian President Petro Poroshenko warned Monday he had no trust in Russia's Vladimir Putin and urged the army to prepare "for the worst" despite a new truce in the separatist east.

The pro-Western Ukrainian leader's comments to servicemen in Kiev came ahead of this week's Defenders of the Fatherland Day -- an occasion of special significance in the post-Soviet republic that views the 18-month uprising in the east as Russian "aggression".

Russian gas giant Gazprom said on Monday it had resumed gas supplies to Ukraine, adding that Moscow had received prepayment of $234 million from Kiev ahead of the winter heating season.

"Gazprom began supplying gas to Ukraine at 10:00 am (0700 GMT) today," Gazprom chief Alexei Miller said in a statement.

President Petro Poroshenko said on Wednesday a "real truce" had begun in eastern Ukraine but a long-lasting peace with pro-Kremlin insurgents would still take some time.

His upbeat comments come with EU nations -- struggling with a migrants crisis -- hoping for signs of a de-escalation after the conflict stoked tensions in eastern Europe.

President Petro Poroshenko has stressed Ukraine must regain control of its eastern border with Russia despite an apparent agreement to push back the implementation of a February peace deal into next year.

The Western-backed leader told Ukrainian television late Sunday that he never agreed to the terms announced by French President Francois Hollande at a media event held after summit talks on the crisis in Paris on Friday.

The leaders of Russia, Ukraine, France and Germany agreed Friday to delay contentious local elections in Ukraine to ensure that they meet international standards, despite fighting having all but stopped in the country's separatist east.

Peace appears closer than ever in the 17-month conflict, which has plunged relations between Moscow and the West to post-Cold War lows, with the latest ceasefire called last month having largely been observed by both pro-Russian rebels and Ukrainian forces.

Kiev said on Wednesday it had struck an initial agreement with pro-Russian insurgents to withdraw smaller weapons from the buffer zone splitting eastern rebel lands from the rest of Ukraine.

International monitors said the two sides' February commitment to pull back heavy weapons from the 500-kilometer (300-mile) line separating the forces was only observed laxly and led to more than 1,000 deaths.

Australia has launched a new bid to be elected to the United Nations Security Council, with Foreign Minister Julie Bishop saying the nation hoped to maintain its focus on international security.

Bishop said in a statement Wednesday that Australia would be a candidate for a Security Council seat in 2029-30 as she signaled the country's intention to also seek a spot on the U.N. Human Rights Council for 2018-20.

Ukrainian President Petro Poroshenko used his speech at the U.N. General Assembly on Tuesday to rail against Russian aggression, urging the world not to believe "conciliatory" statements from his counterpart Vladimir Putin.

The Russian leader called Monday for a broad U.N.-backed coalition to fight the Islamic State group as he seeks to muscle his way back onto the world stage after months of isolation over Ukraine.

Ukrainian pilot Nadiya Savchenko, on trial for the murder of two Russian journalists, said Tuesday she was captured by pro-Kremlin separatists and then smuggled into Russia by armed, masked men.

"I am a prisoner of war and a hostage who has been abducted," Savchenko told the court in a dramatic speech, saying separatist rebels captured her in eastern Ukraine and told her they would "sell" her to Russia.

Ukraine on Tuesday launched the criminal trial of two captured Russian soldiers it claims will prove Moscow's direct but covert involvement in the conflict in the war-torn former Soviet state.

Kiev's forces seized the two wounded men during a May gun battle that violated a ceasefire the warring sides had signed up to under stronger European pressure three months earlier.