The United States said Tuesday it is monitoring North Korea closely and urged that Pyongyang not carry out a fourth nuclear test.

“We have certainly seen the press reports … regarding possible increased activity in North Korea’s nuclear test site,” State Department spokesperson Jen Psaki said during a news briefing.

“We continue to urge North Korea to refrain from actions that threaten regional peace and security and to comply with its international obligations and commitments.”

South Korea’s Defense Ministry spokesman Kim Min-seok had said earlier that activity at Punggye-ri, the North’s main test site, had been increasing as of late.