President Xi Jinping assured President Park Geun-hye of the Republic of Korea during a phone call on Wednesday that Beijing is firmly committed to denuclearization in the Korean Peninsula, a day after Seoul said that the Democratic People's Republic of Korea might be preparing a fourth nuclear test.

China will firmly safeguard the stability of the peninsula while pushing for a peaceful settlement, Xi told Park during the call.

"China stands ready to remain in close communication and coordination with the ROK on peninsula issues, and hopes all relevant parties can work together to reduce tension and safeguard its peace and stability," Xi said.

The ROK's defense ministry said on Tuesday that increased activity at the Punggye-ri site in the DPRK indicated a forthcoming nuclear test.

However, ministry spokesman Kim Min-seok also said it could be a "deception tactic" to raise tensions before US President Barack Obama's arrival in Seoul on Friday.

Obama's weeklong tour of Asia, which started on Wednesday, will take him to Japan, the ROK, Malaysia and the Philippines.

The United States said on Tuesday it was watching Pyongyang's move "very closely".

The US-Korea Institute at the Johns Hopkins School of Advanced International Studies said recent satellite images did indeed show “new operations” at Punggye-ri but a test coinciding with Obama's visit was unlikely.

"Recent operations at Punggye-ri have not reached a high level of intensity in terms of vehicle, personnel and equipment movement that occurred in the weeks prior to past detonations," it said.

"Moreover, other possible indicators present before the North Korean nuclear tests in 2009 and 2013, such as communication vans and a satellite dish intended to transmit pre-test data, have not been spotted."

Park expressed appreciation in the call with Xi for China's attempts to get the DPRK to suspend its testing program, a Seoul official said.

"She asked for further efforts to persuade the DPRK, saying additional nuclear tests would completely alter the region's security map by triggering an arms race and a nuclear domino effect in the region," an official from the Blue House, the president's residence, said.

Xi said it was in everyone's interest to avoid a rise in military tensions on the peninsula.

The DPRK has conducted three rounds of nuclear tests — in 2006, 2009 and 2013 — all at Punggye-ri in the country's northeast.

Zhang Liangui, a Korean studies researcher at the Party School of the Communist Party of China Central Committee, said Pyongyang is unlikely to abandon its nuclear testing, but the timing is not exactly right at the moment to conduct a test.

"It has been the DPRK's national policy to develop nuclear weapons. There is no sign Pyongyang is ready to quit nuclear testing — and actually it is actively preparing for that," Zhang said. "The problem is when exactly the test will come."

Zhang said it's "somewhat farfetched" to talk about a nuclear test during Obama's Asia tour.

"Preparations for a test need lots of time and money. It's not as easy as letting off firecrackers," Zhang said.

Zhang noted that it has been more than one year since the DPRK's last nuclear test, which occurred in February 2013.

"Pyongyang's nuclear technology has improved through its past tests. It is natural for it to reduce the time gap," Zhang said, predicting that the next round of tests might come this year, possibly in October.

During Wednesday's phone call, Park also told Xi that she welcomes him and hopes he will visit her country.

Xi extended condolences to the families of the missing and dead in the ROK's recent ferry tragedy.

Park thanked China for its help and expressed her condolences to the families of Chinese victims involved in the accident. The bodies of two of the four Chinese citizens have been found, while two others remain missing.

Park also expressed her sympathy for relatives of the Chinese passengers on board the missing Malaysian flight MH370.

AFP and Xinhua contributed to this story.