United Nations Secretary-General Antonio Guterres will visit Moscow early next week to meet Russia's President Vladimir Putin and then head to Ukraine for talks with President Volodymyr Zelenskyy.
Mr Guterres will also have a working meeting and lunch with Russian foreign minister Sergei Lavrov, Eri Kaneko, a spokesperson for the UN chief said.
The news comes after the UN documented dozens of civilians killed in the Ukrainian town of Mariupol.
Ukraine's government, emboldened by an influx of Western weaponry, said its beleaguered forces were still holding out inside a sprawling steelworks in the razed port city.
The Kremlin has claimed the "liberation" of Mariupol, the control of which is pivotal to its war plans nearly two months after President Vladimir Putin ordered the shock invasion of Russia's Western-leaning neighbour.
"Since the start of the second phase of the special operation... one of the tasks of the Russian army is to establish full control over the Donbas and southern Ukraine," Major General Rustam Minnekaev said.
"This will provide a land corridor to Crimea," he added, referring to the peninsula Russia annexed from Ukraine in 2014.
Mr Minnekaev's comments were the clearest articulation yet of Russia's goals in the invasion's "second phase", which was forced on the Kremlin after Ukraine's Western-backed resistance around the capital Kyiv.
"This only confirms what I have already said multiple times: Russia's invasion of Ukraine was intended only as a beginning," Mr Zelenskyy said in his regular evening address.
"We will defend ourselves as long as possible... but all the nations who, like us, believe in the victory of life over death must fight with us."
Malcolm Turnbull pushes for tribunal to prosecute Vladimir Putin
Former Australian prime minister Malcolm Turnbull has said a special tribunal he is proposing to prosecute Russian president Vladimir Putin is the only way to assure that he's held accountable for the crime of aggression.
"We'll see no doubt a whole range of Russian commanders brought to justice in the Hague, but the only way we are going to see the man who actually orchestrated this shocking crime brought to account is a tribunal of this kind that Gordon Brown and others and I are proposing," Mr Turnbull told CBC News.
The tribunal was put forth earlier this year by former British prime ministers Gordon Brown and John Major, and former Australian prime ministers Malcolm Turbull and Kevin Rudd.
It will have a limited focus on the crime of aggression, which the former PMs say cannot be addressed by other courts such as the International Criminal Court (ICC), International Court of Justice (ICJ) or the European Convention on Human Rights (ECHR).
Mr Turbull said the Russian president is personally responsible for committing the crime of aggression.
He said previous examples of Mr Putin's aggression include the downing of MH17, crimes committed in Kosovo, and crimes in Sierra Leone.
