Ukraine is coming under pressure from its western backers to adhere to vital structural reforms after Naftogaz, the state oil and gas company and model of reform in recent years, was left without a supervisory board after independent British directors resigned.

The resignations deepened concerns that reforms stipulated by a $17.5bn International Monetary Fund programme risk stalling, after Kiev replenished its coffers on Monday by tapping international markets with a $3bn bond deal. This was the country’s first issue since Russia annexed Crimea in 2014 and fomented war in two eastern regions.

In a letter to management of Naftogaz — Ukraine’s biggest enterprise — Paul Warwick, supervisory board chairman and one of two British nationals to resign this week, wrote: “Despite assurances from senior politicians, deadlines have passed and commitments have not been delivered, with an environment of government control not envisaged in the Corporate Governance Action Plan.”

“Increasing political meddling” had become “increasingly evident and, unfortunately, the norm”, he added.

Three other board members, including a third British national, resigned earlier this year.

The development is a blow to Ukraine’s co-operation with western backers, including the European Bank for Reconstruction and Development, the largest investor in the country, which finances gas purchases for peak winter demand.

Francis Malige, the EBRD’s regional managing director, told reporters in Brussels the situation was a “crisis” and said he understood the resigning board members’ frustration. Mr Malige said the company had been slow to implement agreed reforms. “That needs to be fixed,” he added.

Also speaking in Brussels, Oleksandr Danyliuk, Ukraine’s finance minister, told reporters in Brussels that he was “disappointed at what happened . . . We urgently need a strong, professional supervisory board.”             

The US embassy in Kiev tweeted on Wednesday that a “professional and independent” Naftogaz board was “vital for combating corruption and delivering energy security”. The British embassy said it was concerned by the resignations and Naftogaz was being hindered in realising its potential as a profitable strategic state asset.

Naftogaz was for years lossmaking and a drain on state finances, forced to sell gas bought from Russia at below cost price by state-regulated domestic gas prices. The gas trade was also seen as one of the most corrupt in Ukraine.

Under new management led by chief executive Andriy Kobolev, strongly supported by the board and Kiev’s western backers, Naftogaz has become the country’s most profitable company and largest taxpayer.

The IMF demanded that the government raise domestic gas tariffs towards import prices, and Naftogaz managed to shift from Russian gas purchases to European suppliers. Improved corporate governance at the state company also enhanced efficiency.

But efforts to make Naftogaz less vulnerable to outside influence from politicians and powerful corporate interests in Ukraine have been undermined by official foot-dragging on a corporate governance plan for Naftogaz to appoint a better-functioning board with more independent directors.

As Ukraine Prime Minister Volodymyr Groysman pledged on Wednesday that reforms of Naftogaz and the gas sector would continue, Mr Kobolev urged officials to organise a transparent and competitive tender to appoint new board members.

The Naftogaz chief called for transferring authority over the company to a new board “as stipulated by plans” supported by the country’s backers. He also urged officials to meet an IMF condition by further increasing gas tariffs towards import costs.

Another key test upon which a long-delayed $1.9bn IMF disbursement hangs is the reform of Ukraine’s dysfunctional pension system. Voting in parliament could be held as early as Thursday.

The ruling coalition backing Petro Poroshenko, Ukraine’s pro-western president, has also delayed the formation of an independent anti-corruption court that Kiev’s western backers hope will decisively crack widespread corruption.

In a report entitled “No Sense of Urgency”, Dragon Capital, a Kiev-based investment bank, warned this week: “The slow pace of delivery on programme requirements and the government’s improved FX liquidity following the Eurobond sale make it likely the next [IMF] loan tranche will be delayed further.”