SEOUL, Feb. 18 (UPI) -- North Korea could be planning a "terrorist attack" against the South, Seoul's National Intelligence Service told lawmakers Thursday.
"North Korea's terrorist attack could be in the form of causing harms to anti-North Korean activists, North Korean defectors or government officials," Lee said.
Public safety is a concern, according to the NIS.
Targets of an attack could include "subways, shopping malls, exhibition centers, power plants."
In December, North Korea hacked into a South Korean nuclear power operator, and tensions between Seoul and Pyongyang have grown since the shutdown of a jointly operated factory park in North Korea, the Kaesong Industrial Complex.
Seoul's presidential Blue House has urged for the passage of an anti-terrorism bill that could provide a "legal and institutional framework on anti-terrorism."
"That such a law has not yet been passed is deeply regrettable," said Blue House spokesman Kim Sung-woo, local news outlet Money Today reported.
South Korea's opposition party has criticized the bill, and said it could give more power to Seoul's spy agency.
The terror warning comes at a time when joint U.S.-South Korea forces are preparing for the largest-ever military exercise.
Defense Minister Han Min-koo said Thursday about 15,000 U.S. troops are expected to take part in the annual Key Resolve and Foal Eagle exercises in March, Voice of America reported.
Yonhap reported earlier the nuclear-powered aircraft carrier John C. Stennis is to take part in the drills.
On Wednesday four U.S. F-22 fighter jets flew across South Korea air base.
Lockheed Martin's F-22 Raptor is a powerful aircraft capable of 360-degree midair rotations and can clock up to 8,000 flight hours. It is only one of few aircraft that can supercruise, or keeps up supersonic flight, and can fly at a maximum speed of 1,500 mph.