"One individual has been detained with no further information on that individual. But there are three apparent stabbing victims," said Eric Zahren, a spokesman for the agency. Investigators did not immediately know what prompted the attack, which Zahren said took place in the northeast corner of the park.
The three victims are believed to be tourists. The incident occurred in late morning, and there were many people in the park because of the nice weather.
"Another person might have had their shirt slashed," said Sgt. Scott Fear, a spokesman for the U.S. Park Police, which was also investigating.
"Three of (the victims) were transported to a local hospital and are being treated with non-life-threatening injuries," Fear told CBS affiliate WUSA-TV. He said the area of the attack was closed, but the rest of the park is open.
There was no indication that the acts of violence were related in any way to the White House. The park, which faces the North Portico of the Executive Mansion along Pennsylvania Avenue, historically has been a staging area for protests and demonstrations.