The United States and Cuba are close to a deal on restoring scheduled commercial flights amid the anniversary of detente between the Cold War enemies.
The diplomatic advance would help open the way for US airlines to begin flying to communist Cuba within months in what is likely to be the biggest step towards tighter economic ties since the two countries began normalising 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.
Thursday marks the one-year anniversary of the announcement by US president Barack Obama and Cuban counterpart Raul Castro that the countries were ending a half-century of hostility.
Teams meeting in Washington since Monday "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.
US State Department spokeswoman Kerry Humphrey said the countries "are making progress but still negotiating".
Currently, American and Cuban travellers must fly on charter flights that are expensive and difficult to book, forcing them to buy paper tickets in Cuba or email documents and payment information back and forth with an agent in the US.
Those flying must often arrive at the airport four hours in advance and pay high prices for baggage in excess of strict weight limits.
American officials and aviation executives have speculated that Cuba could allow more than a dozen flights to and from the US a day.
It is unclear if those flights would completely replace charters, but they appear certain to create a surge in travel that would place heavy pressure on Cuba's already overstrained tourist infrastructure. Hotels and private hostals are booked for months.
Authorised American travel to the island is up 50% this year, Jeffrey DeLaurentis, who heads the US embassy in Havana, said. While the majority of US travellers are Cuban-Americans, there has been a sharp rise in Americans travelling for specially authorised purposes, particularly on educational tours known as people-to-people travel.
Among Mr Obama's regulatory changes this year was one permitting such travel to Cuba without specific Treasury Department permission.
Since the announcement last year that the US would establish diplomatic relations and expand trade and tourism with Cuba, major US airlines, including American, Delta, United, JetBlue and Southwest, have expressed interest in establishing regular flights to the island.
Cuba and the US announced last week direct mail service would restart after a 52-year interruption. The governments had been speaking about restoring a postal link since Mr Obama entered office, but those talks stalled when Cuba imprisoned US contractor Alan Gross. He was freed in a prisoner exchange that sparked last year's declaration of detente.
On other issues, however, the US and Cuba remain far apart. These include the billions of dollars in competing property claims, the status of fugitives in both countries, and Cuban protection of human rights.
The nations reopened embassies in each other's capitals this summer.