The United States called on North Korea Tuesday to stop actions that would increase the risk of conflict, after Pyongyang blew up roads linked to South Korea in a rancorous removal of land routes once seen as a symbol of inter-Korean cooperation.

State Department spokesperson Matthew Miller made the call, reiterating Washington's calls for Pyongyang to come back to diplomacy.

"We are monitoring the situation in the DPRK in close coordination with our Republic of Korea allies," he told a press briefing.

"We continue to urge the DPRK to reduce tensions and cease any actions that would increase the risk of conflict, and we encourage the DPRK to return to dialogue and diplomacy," he added.

The Republic of Korea is South Korea's official name, while DPRK is short for the North's official name, the Democratic People's Republic of Korea.

The North carried out the detonations in areas near the Military Demarcation Line separating the two Koreas on Tuesday (Korea time), after its military announced a plan last week to "completely separate" its territory from South Korea in another display of its deepening enmity toward the South, which it has called a "primary foe."

Commenting on the North's recent claim of a South Korean drone infiltration into Pyongyang, Miller restated the US appeal for the North to lower tensions.

"When it comes to the actions by the DPRK, we have seen them continue to take steps that raise tensions," he said. "We will encourage, continue to encourage them to take the opposite path to reduce tensions and stop any actions that could increase the risk of conflict."

The spokesperson also expressed concerns over media reports on the possibility of the North sending troops to Ukraine in support of Russia.

"We are concerned by reports of DPRK soldiers fighting on behalf of Russia," he said.

"If that's true, it would mark a significant increase in the relationship between those two countries, the relationship that you have seen develop over the past several months. It would also indicate a new level of desperation by Russia as it continues to suffer significant casualties on the battlefield."

In an online press briefing, White House National Security Communications Advisor John Kirby said that he cannot confirm those reports, but called reports "concerning."

"This, if true, would represent a significant deepening of that relationship (between the North and Russia). It would also, if true, indicate what I think can only be classified as a new level of desperation by Putin as he continues to try to make progress in Ukraine," Kirby said.

"If it's true, it's coming at a time when Russia continues to suffer extraordinary ... in fact, I would go so far as to say historic levels of casualties in a modern conflict ... I mean, more than 1,000 casualties per day just in recent months." (Yonhap)