North Korea says it will immediately resume "all military measures" the country had suspended under a deal with South Korea following Seoul's decision to partially suspend the agreement.

South Korea on Wednesday suspended part of the 2018 inter-Korean military agreement and resumed reconnaissance and surveillance activities near the demarcation line separating the two Koreas.

The move follows Pyongyang's launch the previous day of what it says is a reconnaissance satellite.

In response, North Korea's defense ministry issued a statement on Thursday via the ruling Workers' Party newspaper, Rodong Sinmun, and other media outlets.

It says the North Korean army will no longer be bound by the 2018 North-South deal.

The measures to be restored include the withdrawal of what Pyongyang calls military steps taken to prevent military tension and conflict on the ground, in the sea and in the air.

The actions also include the deployment of "more powerful armed forces and new-type military hardware in the region along the Military Demarcation Line."

The statement added that South Korea would be held "wholly accountable in case of an irretrievable clash breaks out" with the North.