The United States and Cuba are on the verge of a deal to restore regular airline flights, jump-starting economic relations that have languished despite a year of rapid progress on the diplomatic front, Cuba’s top negotiator said on the eve of the anniversary of detente between the Cold War foes.

The deal being thrashed out at marathon talks in Washington would open the way for U.S. airlines to negotiate with Cuba’s government for routes that could bring thousands more visitors a day to the island. The re-establishment of commercial U.S. flights to Cuba after half a century would be the biggest business development since the two countries began normalizing relations last year.