North Korea's actions taking place along the inter-Korean border are raising the risk of military tensions and miscalculations, a State Department spokesperson said Monday, as the recalcitrant regime began reinstalling guard posts and heavy firearms there.

Seoul's defense ministry has said that North Korean troops were spotted installing temporary guard posts and carrying weapons inside the Demilitarized Zone separating the two Koreas, after Pyongyang declared it would not be bound by a 2018 inter-Korean military tension reduction deal, called the Comprehensive Military Agreement.

"Now, the actions that the DPRK is taking along the DMZ following its abrogation of the CMA are increasing the risk of military tensions and miscalculations on the Korean Peninsula," the spokesperson said via email in response to a question from Yonhap News Agency.

DPRK stands for the North's official name, the Democratic People's Republic of Korea.

"In light of these developments, the United States remains in close and continual contact with the ROK through multiple channels to ensure that our alliance remains in lockstep," the official added, referring to South Korea by its official name, the Republic of Korea.

The North announced its decision to back out of the CMA after the South suspended part of the agreement in response to the North's defiant launch of a space rocket to put a spy satellite into orbit last week. Seoul and Washington view the launch as a violation of UN Security Council resolutions.

The CMA called for demolishing border guard posts within 1 kilometer of the border, banning military drills and maneuvers near the land and sea borders, and establishing no-fly zones along the border, among other measures aimed at reducing cross-border tensions and accidental clashes.

The spokesperson stressed that the North's "escalatory rhetoric and destabilizing actions" inflame tensions in the region but reiterated Washington's openness to engagement with Pyongyang.

"The door has not closed on diplomacy, but Pyongyang must immediately cease its provocative actions and instead choose engagement," the spokesperson said. "In particular, we encourage the DPRK to return to substantive discussions on identifying ways to manage military risks and create lasting peace on the Korean Peninsula."

The official added, "As always, the US commitment to the defense of the ROK remains ironclad."

Touching on the North's launch of the satellite, the spokesperson said that the US' national security team is closely assessing the purported launch in close coordination with US allies and partners.

"We are also watching for any developments in cooperation between the DPRK and Russia on space-related technology transfers," the official said. "The DPRK's developments in its space program have implications for regional and global security, and we call on all nations to abide by relevant UNSC resolutions."

In an apparent message to the US, the North's official Korean Central News Agency said Monday that the spy satellite has taken photos of the White House, the Pentagon and nuclear-powered aircraft carriers docked at a US naval base. (Yonhap)