The UN’s environment chief, under fire over huge travel expenses and rule-breaking, has been forced leave the UN general assembly in New York early and return to his Nairobi headquarters to deal with the growing crisis.

The problems for Erik Solheim, Norwegian head of the UN Environment Programme (Unep), include the Netherlands becoming the latest nation to withhold millions of dollars in funding until the issues are resolved.

The Guardian can also reveal that Solheim has now recused himself from professional dealings with his wife and a Norwegian company that employed her shortly after it signed a deal with Unep in April.

Pressure is growing on Solheim after he was sharply criticised by a draft internal UN audit over his $488,513 globe-trotting travels that called them “contrary to the ethos of carbon emission reduction”. The audit also said he had “no regard for abiding by the set regulations and rules” and that he claimed unjustified expenses.

The UN staff union in Nairobi, where Unep is headquartered, called some of the draft audit’s findings “mind-blowing”. Solheim said he had already paid back money for instances of oversight and that he had made changes where other rules had been broken.

Solheim wrote to all 125 national ambassadors on the committee that oversees Unep’s work on Tuesday to tell them he was cutting short his New York trip and putting in place measures to increase the accountability of managers and their travel. “We will address issues of trust between management, our staff, member states and/or partners,” he said in a letter seen by the Guardian.

Unep is governed by the UN environment assembly, the world’s highest-level decision-making body on the environment. Its president, Siim Kiisler, Estonia’s environment minister, told the Guardian the next steps to be taken would be decided when the internal audit was completed.

“I need to ensure that member states have full trust that their resources are used for the benefit of the environment,” Kiisler said. “I will read the official report carefully, talk to Mr Solheim and after that form a standpoint.”

He said Solheim’s travels had played an important role in making Unep visible, but added: “It certainly has too look and feel right as well, and of course, follow the rules of the system.”

On Wednesday, a spokesman for the Dutch government told the Guardian: “A planned payment of €8m will be held until Unep provides more clarity, and until it is clear that Unep is taking this matter seriously.”

The job taken by Solheim’s wife, Gry Ulverud, is with the Norwegian company X Four-10/REV Ocean, which aims to build the world’s biggest research ship as well as a “World Ocean Headquarter” near Oslo. On 4 May, the company announced a memorandum of understanding with Unep, although Unep did not issue a press release. On 1 June, Ulverud posted on her Facebook page: “Started New Job at at X Four-10/REV – Manager for Strategy and Partnership”. The page has now been removed.

“In relation to any notion of nepotism, I wish to clarify that my spouse was recruited to REV Ocean through an open, transparent and competitive process,” said Solheim. He said her recruitment was based on 25 years of professional experience “with the Norwegian Refugee Council, as a diplomat, as deputy representative to Unesco from 2014-2016 and over 10 years with the Norwegian Ministry of Education and Research.”

Screengrab of Facebook post by Gry Ulverud, wife of Erik Solheim, announcing a new job with X-Four-10/REV Photograph: Handout

Solheim said he wrote to the UN Ethics Office for advice on the matter of his wife’s appointment on 9 July and again on 11 September, when he told it REV Ocean was giving Unep funding over four years.

Solheim said he received the advice on 14 September and wrote to the UN’s secretary general, António Guterres, to recuse himself on 19 September, the same day the Guardian first contacted him on the matter. Solheim said he and Ulverud would have no “direct bilateral interaction” when acting in their official capacities. He said all matters relating to REV Ocean would now be dealt with by the Unep deputy executive director.

The Guardian has also seen emails relating to an initial refusal to allow Ulverud to attend a Unep meeting on marine plastic litter in May, just before she started at REV Ocean. One senior manager advises Ulverud to ask an official for “assistance”. That official then asks colleagues: “Can we think of a creative way to have Gry join the meeting next week?” Ulverud was subsequently invited.

“The available records do not indicate that Ms Ulverud used any influence to obtain access to the meeting other than being an employee of a private sector entity in partnership with Unep,” said Solheim. Her contract started just after the meeting took place, but a Unep spokesman said: “Her employer requested her to do a number of things before assuming her new functions, including attending the meeting in Nairobi.”

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