SOFIA, Bulgaria — While the embassies of most countries promote the interests of companies back home, North Korea’s are in business for themselves.

A series of tough sanctions by the United Nations and an executive order recently signed by President Trump have sought to economically isolate the nuclear-armed regime of Kim Jong-un. But Pyongyang has held on to an array of profit-making ventures, some of which operate in the roughly 40 embassies of the hermit kingdom.

Many of these enterprises are hard to trace, but at least one is impossible to miss. For years, neighbors have complained about the noise coming from a large, fenced-in building here in a southern section of Bulgaria’s capital city. It hosts parties a few times a week, many of them capped off with a late-night flurry of fireworks, shot from the roof.

“It isn’t loud now,” one neighbor, Bonka Nikolova, said as a parade of wedding guests filed into the building. “But if they paid for fireworks, there will be fireworks.”