A THAAD launcher is seen in this photo captured from the Facebook account of the 35th Air Defense Artillery Brigade of U.S. Forces Korea (USFK) on April 24, 2019. Yonhap

The United States is preparing for all contingencies amid signs of a potential North Korean nuclear test but is concerned by Pyongyang's "strengthened rhetoric" around its nuclear program, a state department spokesperson said Thursday.

Vedant Patel, principal deputy spokesperson for the department, said Pyongyang is continuing to prepare for what will be its seventh nuclear test.

"The U.S. assesses the DPRK is preparing its Punggye-ri (nuclear) test site for what would be its seventh nuclear test. This assessment is consistent with the DPRK's own public statements," the spokesperson said in a telephonic press briefing, referring to North Korea by its official name, the Democratic People's Republic of Korea.

"We are preparing for all contingencies in close coordination with our Japanese and ROK allies," Patel added. "Furthermore, we are prepared to make both short and longer term adjustments to our military posture as appropriate in responding to any DPRK provocation."

ROK stands for the Republic of Korea, South Korea's official name.

Seoul and Washington said earlier that the North appeared to have completed "all preparations" for a nuclear test, and that it may only be gauging the timing.

North Korea conducted its sixth and last nuclear test in September 2017.

North Korean leader Kim Jong-un warned his country may use its nuclear weapons against South Korea and the U.S. last month, threatening to "wipe out" the Seoul government and its military should they make what he called a "dangerous move," such as a preemptive strike.

"We are concerned by the regime's strengthened rhetoric around its nuclear program," said the department spokesperson.

"A seventh nuclear test since 2017 would constitute a grave escalatory action, and seriously threaten regional and international stability, as well as security," the spokesperson added.

The department spokesperson also expressed concerns over the health and safety of North Korean people, one day after the North Korean leader declared victory in fight against COVID-19.

"We are very concerned about how COVID-19 could affect the North Korean people and we continue to support the provision of vaccines to the DPRK," the spokesperson said.

Patel urged Pyongyang to work with international aid organizations, noting the North has not accepted any vaccine assistance from the COVAX global vaccine distribution program to date.

"To this end, we strongly support and encourage the efforts of international aid and health organization in seeking to prevent and contain the spread of COVID-19 in the DPRK and to provide other forms of humanitarian assistance to vulnerable groups in the country," he said.

On China's renewed criticism of U.S. THAAD missile defense system deployed in South Korea, the department spokesperson said any such criticism would be "inappropriate."

"The United States and the ROK made an alliance decision to deploy THAAD to the ROK as a purely defensive measure to protect the ROK and its people," said Patel.

"Criticism or pressure on the ROK to abandon its defense is inappropriate," he added. (Yonhap)