A parcel containing a knife, suspicious powder and a threatening letter has been sent to South Korea's defense chief, prompting authorities to launch a probe, the ministry said Friday.

The package addressed to Defense Minister Han Min-koo contained a 32.8-centimeter kitchen knife and some 20 grams of white powder with a two-page letter, according to the ministry, noting that the suspicious powder was later found to be flour.

The letter sent by the "International Peace Action Corps" reads, "Why are you bringing a fire cloud of a nuclear war to the Korean Peninsula by wagging your tongue?," according to the ministry.

"I've decided to punish him out of concern that just leaving you like this would kill the whole people," the letter said, warning to "get rid of" him and his family members.

On one side of the knife, the sender wrote in a red pen, "Han Min-koo," and on the other side, "punishment," the ministry noted.

A joint military-police investigation team confirmed that the parcel was sent via a delivery service at a convenience store in Eunpyeong, northwestern Seoul, with a male suspect in a black shirt and a cap seen sending the package on closed-circuit television footage.

"We will sternly punish such a terror attempt by bringing him to justice in close cooperation with police," ministry spokesman Wi Yong-seop said, adding it opens "every possibility, including the suspect's possible linkage to North Korea."

A deliveryperson first found the knife in the parcel while re-packing the torn box in late August, after learning that the package returned due to an inaccurate address was meant for the defense chief, according to the ministry.

Without a full address, the sender simply put "Han Min-koo" as the recipient name, and the telephone number of the public service center of the defense ministry building in Yonsan, central Seoul, it added.

Last year, a similar parcel with a threatening letter and powder that later turned out to be flour was sent to then defense chief and current National Security Adviser Kim Kwan-jin. The letter threatened to "punish" Kim if he dared to challenge North Korea's "highest dignity" and instigate war. (Yonhap)