The state-owned oil company of Azerbaijan secretly funded an all-expenses-paid trip to a conference in Baku, on the Caspian Sea, in 2013 for 10 members of Congress and 32 staff members, according to a confidential ethics report obtained by The Washington Post. Three former top aides to President Obama appeared as speakers at the event.

Lawmakers and their staff members received hundreds of thousands of dollars’ worth of travel expenses, silk scarves, crystal tea sets and Azerbaijani rugs valued at $2,500 to $10,000, according to the ethics report. Airfare for the lawmakers and some of their spouses cost $112,899, travel invoices show.

The State Oil Company of the Azerbaijan Republic, known as SOCAR, allegedly funneled $750,000 through nonprofit corporations based in the United States to conceal the source of the funding for the conference in the former Soviet republic, according to the 70-page report by the Office of Congressional Ethics, an independent investigative arm of the House.

The report reflects the most extensive investigation undertaken by the ethics office, which was created seven years ago in response to a number of scandals on Capitol Hill, including lobbyist Jack Abramoff’s illegal funding of lawmakers’ trips.

The nonprofit corporations allegedly filed false statements with Congress swearing that they were sponsoring the conference. The findings have been referred to the House Ethics Committee for investigation of possible violations of congressional rules and federal laws that bar foreign governments from trying to influence U.S. policy.

SOCAR released a statement saying that its support of the conference was no secret and blaming the nonprofits for not filing the proper disclosures.

“At no time did SOCAR hide from the attendees of the conference our involvement,” the statement said. “SOCAR has never been under investigation in this matter because the responsibility for disclosing SOCAR’s financial support for the conference fell to those who were the trip’s sponsors.