An Oxford University professor has been accused of selling ancient Bible fragments to a controversial US company that has been involved in several high-profile scandals related to its aggressive purchases of biblical artefacts.

Dirk Obbink, one of the world’s most celebrated classics professors, has been named after an investigation by staff associated with Oxford’s Oxyrhynchus Papyri project.

He is accused of selling without permission a number of ancient fragments to the US arts and crafts chain Hobby Lobby. Its owners, the Green family, are prominent Christian evangelicals and, under the guidance of the Hobby Lobby president, Steve Green, were behind the founding of Washington’s $400m Museum of the Bible in 2017.

A statement published by the Egypt Exploration Society, which manages the Papyri project, claimed it was told by the Museum of the Bible that 11 fragments were sold to it by Obbink in two batches in 2010.

The society and the university confirmed Obbink was under investigation. He continues to be employed at Oxford. The Guardian has contacted him for comment.

The lecturer in papyrology and Greek literature has previously denied some of the allegations, telling the Daily Beast in 2018 that the claim he sold a fragment of the first chapter of the gospel of Mark to Hobby Lobby was not true.

In its statement, the Egypt Exploration Society, which owns the collection and conducted the investigation, said the issue had contributed to Obbink’s removal as general editor of the Oxyrhynchus Papyri project “because of unsatisfactory discharge of his editorial duties, but also because of concerns, which he did not allay, about his alleged involvement in the marketing of ancient texts”.

It added: “In June 2019 the [society] banned him from any access to its collection pending his satisfactory clarification of the 2013 contract [for another fragment sale]. Oxford University is now investigating, with [the society’s help], the removal from university premises and alleged sale of [society] texts.”

The statement said file records relating to the missing fragments had also been removed. “These texts were taken without authorisation from the EES, and in most of the 13 cases the catalogue card and photograph are also missing.”

The statement follows intensive investigations after reports in the Daily Beast this year speculated about the possibility that Obbink had sold a highly prized fragment – if it is real – of the gospel of Mark to Hobby Lobby and the Green family.

The report quoted a blogpost by the New Testament scholar Brent Nongbri, who published an email sent by Michael Holmes of the Museum of the Bible appearing to confirm that “Obbink sold [the fragment of Mark] and three other allegedly early gospel fragments to the Green collection”, adding a copy of the contract.

Commenting after the statement on Monday, Nongbri said: “The sale of the manuscripts and the attempt to cover it up by removing records is almost unbelievable. But the first thing to note are the words ‘so far’. We don’t yet know the full extent of this. More items may well have been sold to Hobby Lobby.”

The Green family and Steve Green have been embroiled in multiple scandals over the long-running programme of purchasing biblical fragments for the Museum of the Bible. According to the Egypt Exploration Society, its investigations have revealed that 13 pieces in the museum’s collection are in fact the rightful property of the nonprofit society.

In a statement, the Museum of the Bible said the antiquities were “sold illegally” by a “known expert”, adding that of the 13 items identified, only four were the property of the museum, with the remainder belonging to Hobby Lobby as part of the Green collection.

The Green family has assembled what it describes as one of the largest collections of biblical antiquities in the world, many of which are on display in the Museum of the Bible.

However, the Greens and the museum have been dogged by controversy over the provenance of some of its acquisitions. In June 2017, Hobby Lobby Stores was ordered to pay a $3m fine for illegally importing thousands of ancient Iraqi artefacts that were falsely labelled and shipped to the company through the United Arab Emirates and Israel.

Commenting after that case Hobby Lobby said it “did not fully appreciate the complexities of the acquisitions process” and relied on dealers who did not understand how to properly ship the items.

In a second high-profile controversy, the Green family and the Museum of the Bible were forced to remove five document fragments – described as part of the Dead Sea Scrolls – when they were identified as modern forgeries after reporting by the Guardian and other media organisations.