Expectations of a breakthrough toward ending the 5-month-old war were boosted a day earlier by Russian President
Poroshenko's own formula for ending the conflict, which he unveiled during his June 7 inauguration speech, requires that the separatists lay down their arms and relinquish seized territory in exchange for negotiations on broader autonomy for their regions within Ukraine.
Both sides said they were prepared to sign a peace deal if their conditions were met during talks in the Belarus capital of Minsk on Friday, when a meeting of the so-called Contact Group on Ukraine convenes.
While Ukrainian authorities in Kiev, the capital, have refused to sit down and negotiate with the rebels they have branded terrorist stooges of the Kremlin, the Contact Group brings together representatives of the government and the separatists, Russia's ambassador to Ukraine and veteran diplomats of the Organization for Security and Cooperation in Europe. OSCE is the only international security forum to which both Russia and Ukraine belong.
"Tomorrow in Minsk a document will be signed providing for the gradual introduction of the Ukrainian peace plan," Poroshenko told reporters on the sidelines of a NATO summit in Wales, where leaders of the Western military alliance expressed solidarity in his fight to keep Ukraine intact.
The fighting in eastern Ukraine, which the United Nations says has taken at least 2,600 lives this year, was sparked by Kiev's westward leanings that the Kremlin and its eastern Ukrainian proxies fear could wrest Ukraine from its historic political alignment and economic integration with Russia.
After Poroshenko's election in May to replace ousted Kremlin ally Viktor Yanukovich as president, he signed an association agreement with the European Union that opens lucrative trade opportunities for Ukrainian goods and allows duty-free imports of European manufacture that Moscow fears will undercut its products.
Poroshenko's meetings with
Russian Foreign Minister Sergei Lavrov accused the West of seeking to torpedo any chance of a peace deal at the Minsk talks by holding out hope of Ukraine eventually gaining membership in the North Atlantic Treaty Organization.
"The surge in anti-Russian rhetoric that we have seen exactly when there is a very active effort to seek a political solution shows that the party of war in Kiev has active external support, in this case from the United States," Lavrov said at a news conference in Moscow.
A separatist leader in Donetsk, the heavily industrialized eastern Ukrainian city that has been in militant hands since April, said his side would stop offensive operations if the government withdraws from the occupied region and shows its commitment to a cease-fire first.
"If there is a real truce on their part, then maybe we will also cease fire," Andrei Purgin, a leader of the so-called Donetsk People's Republic, was quoted as saying by the Interfax news agency. "We will see how they observe their cease-fire."
Poroshenko on Wednesday prematurely announced agreement with Putin on a halt to the fighting, reflecting the growing demoralization of government troops who have suffered major setbacks over the last two weeks.
Ukrainian troops had closed in on the separatists in Donetsk and Luhansk, their last strongholds, last month but were confronted by a massive infusion of Russian troops and armored vehicles that opened a new front against them along the Sea of Azov.
The government's reversed fortunes also followed the arrival of a 280-truck convoy from Moscow to embattled Luhansk, said to be delivering humanitarian aid. But the convoy barged into Ukrainian territory without Kiev's permission to cross the border and before customs officials could inspect most of the vehicles, raising questions about what was delivered.
Satellite images of Russian armored vehicles entering eastern Ukraine have been released by NATO, and elite Russian paratroopers have been captured in the conflict area, bolstering the Ukrainian government's contention that Russia is instigating the unrest.
Ukrainian television on Thursday showed a column of Russian tanks moving toward Mariupol, a port city of 500,000 on the Sea of Azov, which Kiev officials fear is the separatists' next objective in clearing a land corridor from the Russian mainland to Crimea and its strategic military installations.
"We are still witnessing, unfortunately, Russian involvement in destabilizing the situation in eastern Ukraine," he said at the alliance gathering in Wales. "So we continue to call on Russia to pull back its troops from Ukrainian borders, stop the flow of weapons and fighters into Ukraine, stop the support for armed militants in Ukraine and engage in a constructive political process."