Ukrainian President Petro Poroshenko promised after late-night negotiations with Russia's Vladimir Putin in Minsk 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 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 defense 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."
Putin appeared to play down the incident, saying: "I hope in this case there won't be any problems with the Ukrainian side."
Poroshenko, in his opening comments, demanded a halt to arms shipments from Russia to the separatist fighters. He defended a peace plan he issued in June, when the rebels in the southeast Donbass region scorned his invitation to lay down their arms and leave by a safe corridor.
"The prime condition for a stabilization of the situation in Donbass is the establishment of effective control over the Russian-Ukrainian border. It is vital to do everything to stop deliveries of equipment and arms to the fighters," he said.