The US and Cuba have reached an understanding on resuming regular commercial flights between the two countries. Unnamed officials in Cuba and the US said an announcement was imminent.

It is unclear when the flights would start because negotiations between the Cuban government and the US airlines could take months. The move is a significant step nearly a year after the former Cold War enemies began restoring diplomatic relations.

The diplomatic advance would help open the way for U.S. airlines to begin flying to Cuba within months in what would likely be the biggest step toward tighter economic ties since the two countries began normalizing relations last year. Officials on both sides said they had reached an understanding on key points and hoped to reach a formal deal within hours or days.

Teams who have been meeting since Monday in Washington “have made important advances in negotiating a memorandum of understanding on establishing regular flights between Cuba and the United States, and shortly they will be ready to announce a preliminary agreement on this issue,” said Josefina Vidal, head of North American affairs for Cuba’s foreign ministry.

State Department spokeswoman Kerry Humphrey said late Wednesday that the countries “are making progress but still negotiating.”