SEOUL (REUTERS) - South Korea's Unification Ministry on Sunday (June 14) said North Korea should honour past agreements signed between the two countries, a day after Pyongyang warned of retaliatory measures against the south that could involve the military.

"The South and the North should try to honour all inter-Korean agreements reached," the ministry said in a statement. "The government is taking the current situation seriously."

The Defence Ministry said the military is ready to respond to "all situations," and added it is closely monitoring moves by the North Korean military.

Separately, South Korea's National Security Council meeting was held with security and diplomatic chiefs in attendance, "to examine the current situation of the (Korean) peninsula," the presidential Blue House said without elaborating further.

The escalation of tension comes a day ahead of the 20th anniversary of the first inter-Korean summit in 2000, which pledged increased dialogue and cooperation between the two states.

In 2018, the leaders of the two countries signed a declaration agreeing to work for the "complete denuclearisation of the Korean peninsula" and cease "hostile acts."

North Korea said it has been angered by defectors from the North who have been sending back propaganda and food, and in the past week severed inter-Korean hotlines as well as threatening to close a liaison office between the two governments.

Ms Kim Yo Jong, the sister of North Korean leader Kim Jong Un, warned on Saturday of retaliatory measures against South Korea that could involve the military.

As part of the effort to improve ties with the North, South Korean President Moon Jae-in's administration has sought to discourage the leaflet and rice campaigns, and defectors have complained of pressure to avoid criticism of North Korea.