WASHINGTON (Reuters) - Senior Pentagon leaders said on Tuesday that the fast-spreading coronavirus outbreak that has hit the United States could continue for months and that the military would continue to support efforts to counter it for as long as needed.

The coronavirus pandemic has killed more than 660 people in the United States and infected more than 50,000.

President Donald Trump said on Monday he is considering how to reopen the U.S. economy when a 15-day shutdown ends next week, even as the highly contagious coronavirus is spreading rapidly and hospitals are bracing for a wave of virus-related deaths.

“I think we need to plan for this to be a few months long at least and we’re taking all precautionary measures to do that,” U.S. Defense Secretary Mark Esper said when asked how long the outbreak may last and how long the military would continue the support efforts to counter it.

“I am fully confident that at the end of the day, in a period of months, we will get through this,” Esper said during a virtual town hall.

At the same event, the chairman of the Joint Chiefs of Staff, Army General Mark Milley, said that while it was unclear how long the outbreak would last, taking models from the experience of other countries - which may or may not apply to the United States - the outbreak could last into July.

“If it does apply, you’re looking at probably late May, June, something in that range, could be as late as July,” Milley said.

On Monday, Esper announced more security restrictions on those entering the Pentagon. The building has seen a drop in the number of people coming into work since measures to combat the outbreak started, with many of them teleworking.

Esper said that those teleworking should expect to continue to do so for “weeks for sure, maybe months.”

In a sign of the impact the virus was having on the U.S. military, the Navy announced that three sailors had tested positive for the coronavirus aboard the aircraft carrier Theodore Roosevelt, the first known case of the virus aboard a U.S. military ship at sea.

The carrier, which was in the Pacific, was last in port in Vietnam about 15 days ago, naval officials said.

The Pentagon also said that elective surgeries at military treatment facilities, with some exceptions, would be postponed starting March 31.