Ukrainian President Petro Poroshenko promised after late-night negotiations with Russia's Vladimir Putin to work on an urgent ceasefire plan to defuse the separatist conflict in the east of his former Soviet republic.
The first talks between the two leaders since June were described by Putin as positive, but he said it was not for Russia to get into the details of truce terms between the Kiev government and two rebel eastern regions.
"We didn't substantively discuss that, and we, Russia, can't substantively discuss conditions of a ceasefire, of agreements between Kiev, Donetsk and Luhansk. That's not our business, it's up to Ukraine itself," he told reporters early on Wednesday.
"We can only contribute to create a situation of trust for a possible, and in my view, extremely necessary, negotiation process."
Poroshenko, after two hours of one-to-one talks which he described as "very tough and complex", told reporters: "A roadmap will be prepared in order to achieve as soon as possible a ceasefire regime which absolutely must be bilateral in character."
Despite the positive tone, it remained unclear how the rebels would respond to the idea of a ceasefire, how soon it could be agreed and how long it might stick.
And with Putin insisting the details were an internal matter for Kiev, there was no sign of progress on a fundamental point of disagreement: Ukraine's charges that Moscow is sending arms and fighters to help the rebels, and Russia's adamant denials.
The leaders shook hands at the start of their meeting in the Belarussian capital Minsk just hours after Kiev said it had captured Russian soldiers on a "special mission" on Ukrainian territory.
Responding to a video of the detained servicemen, a Russian defence ministry source told Russian news agencies that they had crossed the border by mistake. But Ukraine's military spokesman dismissed that, mocking the idea that "the paratroopers got lost like Little Red Riding Hood in the forest".
The Minsk talks, preceded by six hours of wider negotiations with top European Union officials and the presidents of Belarus and Kazakhstan, were aimed at ending five months of conflict that has heightened tensions between Russia and NATO, prompting both to step up military manoeuvres.
A United Nations report obtained by Reuters said more than 2,200 people have been killed, not including the 298 passengers and crew who died when a Malaysian airliner was shot down over rebel-held territory in July.
The crisis has prompted the United States and EU