WASHINGTON -- The United States says another two Americans are confirmed to have suffered health effects from mysterious incidents in Cuba that Secretary of State Rex Tillerson has called "health attacks."

State Department spokeswoman Heather Nauert says the total of Americans affected has climbed from 19 to 21.

The additional two appear to be newly reported cases that occurred in the past. The U.S. says there have been no new "incidents" since August. The State Department disclosed the August incident earlier this month.

The U.S. has said it still doesn't know what caused the attacks or who perpetrated them. Diplomats posted to the U.S. Embassy in Havana started reporting symptoms last November. The incidents stopped for some time before resuming.

The incidents caused concussions and permanent hearing loss, plus other symptoms.