WASHINGTON (AP) — The Homeland Security Department has ordered agents at airports and other ports of entry to observe everyone coming into the United States for potential signs of Ebola infection, officials said Wednesday. They did not provide immediate details or say what specific measures would be taken.

Homeland Security Deputy Secretary Alejandro Mayorkas said Customs and Border Protection agents are also handing out fact sheets to travelers with details of what symptoms to look for and directions to call a doctor if they become sick within 21 days.

Mayorkas did not elaborate on how they would observe people or say when the new measures would begin. He said agents would observe all travelers for "general signs of illness" at the points of entry. He spoke at an airport security conference in Northern Virginia on Wednesday.

The Obama administration has wrestled in recent weeks with what it can do effectively to detect arriving passengers who may be carrying the disease since many of them may not be symptomatic when they arrive.

Mayorkas said the department was aware of those issues and is "taking a layered approach."

A Liberian man is in critical condition with Ebola at a Dallas hospital. He came to Dallas in late September but did not at the time he entered the U.S. display any physical signs of having the disease.

Ebola has killed more than 3,400 people in West Africa and infected at least twice that many, according to the World Health Organization. The virus has taken an especially devastating toll on health care workers, sickening or killing more than 370 of them in the hardest-hit countries of Liberia, Guinea and Sierra Leone — places that already were short on doctors and nurses before Ebola.

President Barack Obama has said the U.S. will be "working on protocols to do additional passenger screening both at the source and here in the United States." Extra screening measures are in effect at certain airports in the affected countries. In Liberia, passengers leaving the country are screened for fever and asked if they have had contact with anyone infected with the disease.

Dr. Tom Frieden of the Centers for Disease Control and Prevention, said this week that officials are looking at all options "to see what we can do to increase safety of all Americans."