The four leaders spoke shortly after Russia said it may resume gas deliveries to Ukraine next week if Kiev pays £1.4 billion in unpaid bills and advanced payments.
The breakthrough follows a series of European brokered talks between the two sides to get gas flowing in time for winter.
Gazprom, the Russian gas monopoly, halted supplies to Ukraine in June amid a dispute over unpaid depts.
The United States said earlier this week that it would not recognise any poll not agreed with the Ukrainian government in Kiev.
Russia has already said it will recognise the results of the election, framing them as legitimate under the Minsk protocol.
Voters will be asked to elect heads of government in the self-proclaimed Donetsk and Luhansk People’s republics, as well as members of parliamentary assemblies that have been dubbed “Supreme Soviet”.
Ukraine has condemned the elections as a flagrant violation of September 5 Minsk protocol, a 12-point plan that led to a ceasefire and was mean to signed by both sides that was meant to lead to an end to the fighting.
The protocol calls for local elections in eastern Ukraine, but only in accordance with a Ukrainian law granting the break-away regions a special autonomous status within the country - effectively guaranteeing Ukraine’s territorial integrity.
Sunday’s elections are not being held in accordance with the special status law, however, and separatist leaders have said that they are seeking to build an independent break-away state.
Alexander Zakharchenko, the “prime minister” of the self-declared Donetsk People’s Republic told a Russian magazine last month that he felt pressured into signing the agreement and considered it an act of treachery.
Mr Zakharchenko is one of three candidates running for the post of head of government, and considered almost certain to be renamed head of the republic after Sunday’s vote.
He has since said he wants to recapture Slavyansk and Kramatorsk, which have been under Ukrainian control since June, and to capture the strategic sea port of Mariupol.
Although he later clarified that he wished to achieve this through peaceful means, he hinted the military option remains on the table.
“We are negotiating about Mariupol peacefully - [the government] does not want to. If the peaceful route fails, we will use force,” he said during a campaign stop on Thursday, Russia’s RIA Novosti news agency reported.
Separatist leaders say they consider the entire Ukrainian administrative regions of Donetsk and Luhansk as their legitimate territory, raising suspicions that a major offensive may be planned following the vote.
More than 3,700 people have died in the conflict in eastern Ukraine, which began after pro-Russian separatists seized control of government buildings in several towns in April.
A ceasefire signed last month has slowed but not stopped the fighting, with fierce battles continuing at flash points including Donetsk Airport, Mariupol, and the town of Debaltsevo.
Heavy shelling was audible from the city centre in the direction of the airport on Friday, where separatist forces are trying to dislodge a Ukrainian garrison.
Western and Ukrainian officials say Russia has provided weapons, ammunition, and troops to the separatists throughout the six month war.
Russia denies any military involvement in the conflict.
By Roland Oliphant
