"That's one of the paths that's being looked at and considered."
The US is considering making Covid-19 vaccinations a requirement for foreign travellers, the White House has said.
Due to the prevalence of the Delta variant, the US Centers for Disease Control and Prevention (CDC) currently recommends that people do not travel internationally until they are fully vaccinated.
Travel advisories, meanwhile, remain in place for the majority of foreign destinations for Americans, including Ireland.
White House Covid-19 response co-ordinator Jeff Zients said on Thursday that while the administration understands the importance of international travel, the prevalence of the Delta variant means the US will maintain existing travel restrictions at this point.
Speaking at a White House Covid-19 briefing, he added: "We do have... agency working groups that are developing plans for when we do open travel - how do we do it in a consistent and safe way.
"Part of that planning is a phased approach that foreign nationals travelling to the United States may - there's still policy work being done here - may need to have some type of vaccine requirement.
"But that's not a decision at this point. That's one of the paths that's being looked at and considered.
"But there are alternative paths being looked at at the same time.
"So, the inter-agency working groups are currently developing a policy process and we will be ready when it is the right time to consider reopening travel."
Zients added that the return of US international travel will be guided by "the science and the public health".
