A top Democrat has demanded answers after it was reported that a Russian oligarch close to Vladimir Putin paid hundreds of thousands of dollars toward Donald Trump Jr’s wedding in the Bahamas earlier this year.

Trump Jr, the US president’s eldest child, married Palm Beach socialite Bettina Anderson in a lavish three-day celebration across two exclusive private islands in May, which according to ProPublica was partially bankrolled by Umar Kremlev, a member of the Russian president’s circle.

Citing records and interviews with three anonymous sources familiar with the event, ProPublica reported that Kremlev footed the bill to rent one of the islands where a reception was held and where guests slept, along with other large expenses, including a huge firework show.

“Why did a Russian oligarch close to Putin fund Trump Jr.’s wedding in the Bahamas?” posted Robert Garcia, the ranking member and lead Democrat on the House oversight committee, on social media. “Umar Kremlev spent hundreds of thousands of dollars on the President’s son. What did he get in return? We need answers.”

Kremlev has a longstanding relationship with Putin. He is the head of the International Boxing Association (IBA), a sporting body that has been backed by the state-owned Russian energy company Gazprom. According to ProPublica, the wedding payments came from an IBA-affiliated entity in Dubai that the boxing association uses for financial transactions.

In the days before the wedding party, he reportedly went to China as part of a delegation accompanying Putin, and the month prior the Russian president had bestowed him with a state honor, the Order of Friendship. The Ukrainian government has imposed sanctions on Kremlev, citing his closeness to Putin and Russian security services.

Alexander Lagutin, a businessperson who has held senior roles at a Russian defense contractor and a state-backed energy company, had been with Kremlev on the China trip. Kremlev’s right hand at the IBA, Elena Sobol, attended the wedding, too.

While the event was extravagant, the guest list was intimate, with only about 50 people attending, most of whom were immediate family, close friends and business partners of the couple. Then there was Kremlev, who reportedly didn’t attend the ceremony itself, which was limited to just 18 guests, but was present with a large contingent of Russians at the party, much to the confusion of the other guests. The group reportedly sometimes stood off by themselves speaking Russian, according to ProPublica.

The affair has raised questions about the implications of a member of Putin’s circle financially supporting and gaining such intimate access to the US president’s family. In recent years Trump Jr has emerged as a leading campaign surrogate for Trump and has even been touted as a potential political heir.

Retired FBI official Frank Montoya Jr told ProPublica: “If I’m paying for your wedding, at some point, you’re going to owe me something. This should be unthinkable for the son of the president.”

It remains unclear why Kremlev helped pay for the wedding and why he was there, when he appears to have only met Trump Jr – the executive vice-president of the Trump Organization, who has a personal net worth somewhere in the ballpark of $300m – quite recently.

Donald Trump famously didn’t attend the wedding. “He’d like me to go, but it’s going to be just a small, little private affair,” the US president told reporters a few days before the nuptials. “I said, you know, this is not good timing for me. I have a thing called Iran and other things.”

In response to detailed questions from ProPublica, a spokesperson for Trump Jr did not deny that Kremlev had helped fund the wedding. “Umar is a personal friend of Don,” the spokesperson said, adding Kremlev is “not someone he has a business relationship with” and that the men met through a mutual friend in the hunting world.

After the article was published, Bettina Trump also confirmed the report, thanking “our dear friend Umar” who “very generously hosted two incredible nights of celebrations for us AFTER our wedding”.

In the post, signed by the couple, she said she and Trump Jr “got married privately on” 22 May “surrounded ONLY by our family”, and characterized the Russian businessman’s role in the post-wedding festivities as a gift.

“It was an extraordinarily generous wedding gift from a friend, and something for which we were and remain incredibly grateful,” she wrote, later adding: “Friendship doesn’t require a political motive. Generosity doesn’t automatically come with an agenda. And sometimes a wedding gift is simply a wedding gift.”