Seoul says North Korea has repeatedly staged cyberattacks on South Korean business and government websites.
A South Korean defense ministry source said on Tuesday morning that the country's military was closely watching movements in North Korea and is fully prepared.
US President Donald Trump, it seems, badly wants to go war with North Korea.
North Korea has been found responsible for a number of high-profile attacks over the years, and is still technically at war with the United States and South Korea.
A North Korean known only as "Kim" was allegedly paid to carry out an attack with biochemical substances but was foiled, a statement by the North Korean ministry of state security said.
Kim Jong Un's half-brother, Kim Jong-nam, who had publicly spoken out against the Kim family's dynastic control, was assassinated in dramatic fashion previous year , while the ruler's uncle, Jang Song Thaek, was executed in 2013.
South Korean and US forces are maintaining a bolstered defense posture as the North could carry out provocations around the Worker's Party anniversary or the Chinese party event. It will also take North Korea some time to hold meetings and reach its decision.
The past several weeks covering Mr. Trumps remarks pertaining to North Korea, its NOT ruled out that military action could be used.
Mr Trump is expected to send a "significant message" to North Korea either verbally or "kinetically" during the trip, Yonhap said, without elaborating on what that may mean.
North Korean men and women participate in a mass dance event marking the 20th anniversary of the election of former leader Kim Jong Il as general secretary of the Workers' Party.
North Korea launched a missile over Japan, an ally of the United States, on September 15, and on August 25, launched three missiles into the sea between Japan and the Korean Peninsula.
Do you believe tonight will be the start of a war between the United States and North Korea?