Naftogaz Ukrainy may file a lawsuit against Gazprom in Stockholm arbitration next week, Justice Minister Pavlo Petrenko said in an interview with RBC-Ukraine on Thursday.

"Ukraine has served Gazprom with a pre-arbitration statement with the clearly defined issues, which, in our opinion, are in dispute. The 30-day term during which Gazprom may agree to the pre-arbitration proposal expires on May 29. Accordingly, taking into account the position that they will be final, we will finalize our lawsuit. Hypothetically, if Gazprom agrees to our claims, that would be one situation; if not, then it unambiguously means a lawsuit," he said.

Naftogaz Ukrainy is preparing the lawsuit itself with assistance from the Justice Ministry, he said.

"The drafting of the lawsuit is in the final stage. We are interested in filing the lawsuit as soon as possible. Given the Stockholm arbitration procedures, I think this will require about a week," he said.

Ukrainian Energy and Coal Industry Minister Yuriy Prodan said previously that Naftogaz would file a lawsuit in Stockholm arbitration on May 28 contesting the price in the gas contract with Gazprom.

In mid-May, Gazprom notified Naftogaz that beginning with June it must prepay for gas and presented a bill of $1.66 billion for gas deliveries in June that must be paid by June 2.