The U.S. is developing a plan to require almost all foreign visitors to be fully vaccinated against COVID-19 as part of eventually lifting travel restrictions that bar much of the world from entering the country, a White House official said on Wednesday.

The White House wants to reopen travel, which would boost business for the airlines and tourism industry, but it is not ready to immediately lift restrictions because of the rising COVID-19 caseload and highly transmissible COVID-19 Delta variant, the unnamed official said.

The Biden administration has interagency working groups working "to have a new system ready for when we can reopen travel," the official said, adding that it includes "a phased approach that over time will mean, with limited exceptions, that foreign nationals traveling to the United States (from all countries) need to be fully vaccinated."

The first round of travel restrictions was imposed on China in January 2020. Numerous other countries have been added, most recently India in May.

The official's comments were the strongest signal to date that the White House sees a path to unwinding those restrictions.

Last month, the White House was considering requiring foreign visitors to be vaccinated as part of discussions on how to relax travel restrictions.

The official said the "working groups are developing a policy and planning process to be prepared for when the time is right to transition to this new system."

Some countries, including Canada and the United Kingdom, are relaxing or lifting restrictions for vaccinated Americans to travel.

The White House interagency talks had previously focused on requiring vaccines for nearly all foreign visitors arriving by air. The White House official did not immediately answer questions about whether the administration is developing plans to also require visitors arriving from Mexico and Canada to be vaccinated before crossing land borders.

Currently, the only foreign travelers allowed to cross by land into the United States from Mexico and Canada are essential workers such as truck drivers or nurses.

It was not clear how long the administration would maintain existing restrictions. But the official reiterated that infections "appear likely to continue to increase in the weeks ahead" and that "the United States will maintain existing travel restrictions at this point."

The Biden administration has also been talking to U.S. airlines in recent weeks about establishing international contact tracing for passengers before lifting travel restrictions.

(With input from Reuters)