European Union nations could block visitors from countries with severe coronavirus outbreaks, including the United States, according to officials involved in the talks.

As European countries prepare to reopen their borders to international travel, officials at the European Commission have been working with member states on advising which visitors might be considered safe to visit from July 1.

While multiple sources told CNN they had not seen lists of specific countries, officials said they were working on criteria that would be used to draw up guidance. Discussions were ongoing, the sources said.

The guidance will be based on how countries of origin are managing the coronavirus pandemic, at a time when some parts of the world are seeing cases surge. "The criteria will be focused on circulation of the virus," said one EU diplomat, adding that Brussels is looking to keep out travelers from countries "where the virus is circulating most actively."

Recommendations made by the European Commission are not mandatory -- decisions on whether and how to open up borders are matters for individual states.

When asked if the US was on a list of origin countries that might be barred from travel to Europe, one EU diplomat directed CNN to the first point of a June 11 checklist published by the European Commission on what to consider when allowing travelers into the EU.

The first point on the checklist asks whether the country can "be considered as being in a comparable or better epidemiological situation as the average in the EU+ area" with regard to number of new infections, trend of new infections and response in areas such as testing, surveillance, contact tracing, containment, treatment and reporting.

The U.S. has the highest number of coronavirus deaths and infections in the world. As of late Tuesday in the U.S., at least 2,346,937 had been infected in the country and 121,224 had died, according to the Johns Hopkins University Coronavirus Resource Center.

The EU diplomat added that some European countries were "reticent about reopening at all," for fear of unleashing a second wave of coronavirus infection.

U.S. travel restrictions could vary by region

The New York Times reported on Tuesday that Americans might not be able to travel to the European bloc when it reopens its borders. The paper said it had seen draft lists of countries considered acceptable or not, based on their coronavirus situation.

A State Department spokesperson told CNN: "We are committed to coordinating with our European partners and allies as we look forward to reopening our economies and easing restrictions. We continue to urge US citizens to check the websites of the relevant US embassy or consulate websites for information on entry restrictions, foreign quarantine policies, and urgent health information provided by local governments."

Among the options being discussed are travel restrictions based on US geographic regions, rather than a sweeping ban on the entire country, since some regions have higher infection rates than others, two EU officials told CNN.

Another EU diplomat told CNN that the permanent representatives of the EU member states to the European Union had discussed this issue Monday and would discuss it again Wednesday. The diplomat said they had not seen a list of countries, only of criteria. Included in those criteria is the incidence of coronavirus per 100,000 people over the past 14 days.

Reciprocity is also a consideration, the EU diplomat added. Earlier this year, the U.S. severely restricted travel from large parts of Europe due to coronavirus concerns.

The White House has thus far shown very little interest in engaging on the issue, according to two European officials. "The US travel ban is far more strict, so it's hard to imagine them putting up a fuss for this, and they haven't," a senior European official said.

'We need to keep our citizens safe'

A third European diplomat said that the travel ban under discussion has nothing to do with the executive order signed by U.S. President Donald Trump this week that freezes visas for foreign workers. "It's purely based on health considerations," this person said.

Another EU official echoed that view. "This has been hiding in plain sight since 11 June, when we published the criteria. This is nothing new in the story for the U.S.," the official said.

"This has absolutely nothing to do with political decisions, this is based on the current health situation in a third country. I know some media have said for instance the executive order the United States President signed is part of this decision; it could not be further from the situation."

Europe is the world's biggest vacation destination, according to EU figures, and tourism accounts for 10% of Europe's GDP. "We are keen, and member states are keen for Europe to be open for tourism, for jobs," said the official.

A fourth EU diplomat said the 27 countries around the table were discussing the quality of data the EU was receiving on countries' testing regimes, as well as the criteria countries must meet. "Our first priority is we are in a pandemic, and we need to keep our citizens safe," the diplomat said.

"We are working to an agreement that would allow us to coordinate the opening of the borders and we are discussing which countries are going to be allowed in first, and this is a positive list, we want people to come."

The European Commission, which is tasked with revising the checklist criteria, is "working around the clock" to get the guidelines back to member states as quickly as possible ahead of the scheduled July 1 reopening, according an official at the Commission.

Ambassadors are set to meet again on Friday to discuss the next steps in the process.