South Korea's defence minister received Tuesday a package containing a threatening letter and suspicious powder, in what his ministry described as an attempted act of "terror".
The parcel was delivered a day after hundreds of threatening leaflets were found scattered outside Defence Minister Kim Kwan-Jin's office.
The leaflets condemned Kim for his perceived hardline stance against North Korea, which has made the minister a focus of Pyongyang's more vitriolic propaganda attacks on the South.
"The parcel contained suspicious white powder, and an investigation is under way to trace its origins," a defence ministry spokesman told AFP.
It was "an attempted act of terror", the spokesman said, while stressing that the powder's contents had not been verified yet.
The Korean peninsula has been in a state of heightened military tension since the North carried out its third nuclear test in February.
Incensed by fresh UN sanctions and joint South Korea-US military exercises, Pyongyang has spent weeks issuing blistering threats of missile strikes and nuclear war.
Pictures recently released by the official Korean Central News Agency showed North Korean military attack dogs tearing at a mannequin masked with a photograph of Kim's face.