READ: President Trump's Letter To Governors On New Coronavirus Guidelines

President Trump said in a letter to U.S. governors on Thursday that his administration is working to publish new guidelines for state and local governments to use when making decisions about "maintaining, increasing or relaxing social distancing and other mitigation measures" for the coronavirus epidemic.

Trump said officials are gathering testing data that will suggest guidelines categorizing counties as "high risk, medium risk or low risk" for the virus. The data will drive "the next phase" of the response, he said.

Trump has indicated that he wants to adjust his 15-day social distancing guidelines so that more parts of the stalled U.S. economy can reopen by April 12. The 15th day of the original guidelines is Monday.

Read the full letter below, or click here:

Trump's new letter echoes recent comments about the use of data made by his top advisers in recent days. On Tuesday, Dr. Anthony Fauci of the National Institutes of Health, told the White House briefing that testing "has really changed the complexion of the approach that we're going to be able to take."

Fauci told NPR's Noel King on Morning Edition on Thursday that the increased testing could help parts of the country not experiencing mass outbreaks to identify, test, trace and isolate cases. "We are quickly getting to the point where we will be able to get that data," Fauci said.

But he acknowledged that more testing is still needed. "To be honest, we don't have all that data now uniformly throughout the country to make those determinations. But that's a major, primary goal that we have right now, is to get those data, because you have to make informed decisions and your decisions are informed by the information you have," he said.

Trump held a videoconference call with governors on Thursday, and the White House is slated to give a briefing on the virus at 5 p.m. ET.