India, Sept. 29 -- US Ambassador to Greece Kimberly Guilfoyle is at the center of a controversy over her links to Greek company Aktor Group. As she works to help European countries buy US natural gas, her close association with the company and its lobbyist Christos Marafatsos has drawn attention. Here's what we know about the controversy.

According to The Wall Street Journal, Guilfoyle has been pushing European governments to buy US liquefied natural gas as part of a "vertical gas corridor" meant to move gas away from Russia. But she has repeatedly promoted one specific company, Aktor Group, a newcomer to the gas business.

In Bulgaria, Guilfoyle told the government that it should work with Aktor. A person familiar with the talks said, a...