Stoltenberg's visit comes just days after Ukraine and the separatists began pulling back weaponry from one front line in the east. The disengagement in two locations is seen as the final hurdle before much-anticipated peace talks between the leaders of Ukraine, Russia, France and Germany that aim to finally end the deadly conflict.
The weaponry pullback finally began Tuesday after Zelenskiy, who won office in April on a pledge to end the war, visited the area around the eastern village of Zolote and confronted armed veterans who came there to try to hamper the weapons pullback.
Zelenskiy told reporters Thursday that Ukraine will start a pullback from the second location, Petrovske, on Monday if a cease-fire persists. The armed conflict in Ukraine's former industrial heartland has killed more than 13,000 people since 2014 and left large swathes of land, including two regional capitals, in the hands of separatist rebels. It began after Russia annexed the Crimean Peninsula from Ukraine in 2014.
Russian President Vladimir Putin said Wednesday that he was open to the four-way summit on eastern Ukraine but he would wait for the weapons pullback to be completed. Ukraine and the West have accused Russia of propping up separatists with funds, weapons and sometimes by sending in troops across the border. The U.S. and the European Union have introduced several waves of sanctions against Russia for its action in Ukraine. The sanctions have badly hurt the Russian economy, and the EU has linked the prospect of lifting them to a peaceful settlement in eastern Ukraine.
Russian Foreign Minister Sergey Lavrov said Thursday that Moscow supports Zelenskiy's moves to pull back weapons and secure a lasting cease-fire in the east. He added the weapons pullback should eventually go along the entire front line.
"We hope that President Zelenskiy will ensure the fulfillment of his orders," Lavrov said at a news conference after talks in Moscow with Thomas Greminger, chief of the Organization for Security and Cooperation in Europe.
Vladimir Isachenkov in Moscow contributed to this report.