Infrared thermal cameras picked up signs that North Korea could have been unilaterally resuming factory operations at the suspended inter-Korean industrial park, a breach of an agreement that South Korea says will have consequences.

At least four factories in the Kaeseong Industrial Complex seem to be in operation, according to Radio Free Asia. It said Tuesday that factory activity at one of those plants, which makes rice cookers, looks exceptionally high, citing an expert on satellite images.

The jointly run park had been home to South Korean companies employing North Korean workers until February 2016, when Seoul shut it down to sanction Pyongyang following its nuclear and missile tests that year.

A week ago, South Korean Unification Minister Kwon Young-se, who handles inter-Korean affairs, publicly warned North Korea of repercussions should they continue using the park without Seoul’s permission, calling Pyongyang “irresponsible” for not picking up the regular hotline calls.

Kwon’s April 11 statement was the first of its kind in 13 years that came four days after the North refused to answer the routine daily calls meant to check in and prevent unwarranted spillovers from skirmishes. The Unification Ministry had sent over a notice demanding the North stop running the park before Pyongyang went unresponsive.

“We’re are closely looking at legal options and we will seek whatever damages our companies there face ... even if that takes time,” a senior Unification Ministry official said Tuesday. The official declined to reveal any specific “legal steps that could follow,” repeating that everything was under scrutiny.

Whether efforts are underway to make the case international is “hard to tell right now,” the official added, without elaborating. Few expect the North to heed South’s request, even if it carries international support, given that the North is in the middle of a prolonged campaign of aggression.

On Saturday, South Korea fired warning shots at a North Korean patrol boat that crossed the maritime border in the West Sea. Any calibrated provocation is ruled out, but the incident was a reminder of a West Sea confrontation that last took place in October. Then, the two Koreas traded warning shots, with the South firing 20 artillery shells to ward off a North Korean commercial vessel.

North Korea’s solid-fuel intercontinental ballistic missile launch on Thursday, however, again put any efforts to bring North Korea back to the nuclear dialogue to the test. The latest weapon fires quicker and is harder to detect -- a significant advance in technology experts say makes North Korea’s nuclear attacks more lethal.

South Korea and the US will hold a summit in Washington next week to mainly discuss North Korea’s disarmament.