South Korea says a threatening letter containing a suspicious powder was sent to Seoul's defense minister, in what the government is calling an attempted act of terror.
Investigators said Tuesday they are working to identify the nature of the white powder found in the letter. It is not known whether it posed a danger to Defense Minister Kim Kwan-jin.
Officials say the letter is similar to the hundreds of leaflets scattered last week near the defense ministry that threatened to "punish" Kim for what it said was his tough stance on North Korea.
The North has repeatedly threatened to attack the South because of the annual U.S.-South Korean military drills and United Nations sanctions that were passed in response to its February nuclear test.
Pyongyang has gradually reduced its harsh war rhetoric in recent days. Last week, it outlined the conditions it said were necessary to engage in dialogue with Washington, but insisted it will not abandon its nuclear program.
Many analysts say there is no evidence North Korea intends to follow through on its threats of missile attacks and nuclear war. But Seoul has recently blamed the North for a computer attack last month that shut down thousands of computers at South Korean banks and broadcasters.
The two countries have been in a technical state of war for more than 60 years. The agreement that ended the 1950 to 1953 civil war hostilities was only a truce.