The Pentagon said the unnamed U.S. national was taking shelter and suffered a "cardiac episode," dying shortly thereafter. The attack followed U.S. strikes against Iran-backed militants last week.

"The last thing — the last thing — we need is Neanderthal thinking that in the meantime, everything's fine, take off your masks. Forget it, it still matters," Biden said.

New York Gov. Andrew Cuomo apologized for making people feel uncomfortable, but said he would not resign and urged people to wait for the attorney general's investigation before forming opinions.

Moderate Democrats have demanded that the $1,400 stimulus checks be targeted at low- and moderate-income people. The change, if adopted, means the House will need to vote again on the package.