The talks are to take place in Brussels, the source said on Friday.
The European Commission does not rule out that the Ukrainian and Russian gas companies may resume contacts this weekend.
The source expressed hope that the parties would put forth any concrete proposals at the tripartite meeting.
At the same time, he declined to elaborate.
On Tuesday, June 3, Gazprom and Naftogaz of Ukraine agreed to negotiate bilaterally, without further mediation by the EU. Ukraine insists on the recalculation of its debt for the gas supplied in 2013 on the basis of a discounted price of $268.5 per 1,000 cubic metres for January-March.
On April 30 Ukraine’s debt reached 3.5 billion dollars.
On April 1, Gazprom cancelled two discounts and raised the price for Ukraine to 485.5 dollars per 1,000 cubic metres.
The throughput capacity of the Ukrainian gas transportation is 288 billion cubic metres system at the entrance and 178.5 billion cubic meters at the exit, including 142.5 billion cubic metres to European countries and 3.5 billion cubic metres to Moldova.
Ukraine’s gas transportation system consists of 72 compressor stations, 110 production shops and 1,451 gas distribution stations. The overall length of gas pipelines operated by the company is 38,600 kilometres, including 22,200 kilometres of trunk pipelines and 16,400 kilometres of extensions.