Peace negotiations in Minsk have continued through the night and into Thursday morning. The German, French, Russian and Ukrainian leaders moved their talks to a private session among themselves, away from diplomats.
The four leaders met in Belarus on Wednesday after an extensive diplomatic push by Angela Merkel and Francois Hollande, whose meeting last week with Ukraine's Petro Poroshenko and Russia's Vladimir Putin paved the way for these latest Minsk talks.
The leaders first met privately, before opening the format to include foreign ministers and other diplomats. After some time, they reverted to the smaller group again.
Russian Foreign Minister Sergei Lavrov is said to have described the talks so far as "better than super," according to Moscow's Interfax news agency.
In addition to a lasting ceasefire, one of the main issues being discussed is a new line of division - Ukraine wants the one agreed to in the previous Minsk accord last September, while Russia wants one that reflects territorial gains made by the separatists.
Other sticking points are the withdrawal of Russian troops and equipment from eastern Ukraine - the existence of which Moscow has always denied - as well as securing the mutual border of Ukraine and Russia. Ukraine has also said it may give the separatists broader legal rights, but Russia wants guarantees of greater autonomy.
Under last September's agreement, both sides agreed to a ceasefire and the withdrawal of "illegal armed groups, military hardware, and all fighters and mercenaries" from Ukraine. The agreement, however, failed to stop the conflict.
Ukraine and the West have accused Moscow of furthering the conflict in eastern Ukraine by supplying the separatists with troops and weapons - charges the Kremlin has denied.
These latest talks come as dozens of people were reported killed in eastern Ukraine on Wednesday, largely due to shelling of residential areas in the city of Donetsk. There were also rocket attacks reported in the city of Kramatorsk on Tuesday.
News agency dpa reported that two top leaders among the Ukrainian separatists, Alexander Zakharchenko and Igor Plotnitsky, also arrived in Minsk on Wednesday.
The UN estimates that almost 5,400 people have been killed since the fighting in the eastern Ukrainian regions of Donetsk and Luhansk broke out in April, following Russia's annexation of Ukraine's Crimean Peninsula.
jr/msh (dpa, AP)