US Defense Secretary Jim Mattis said the DPRK will receive relief only after it takes clear and irreversible steps to end its nuclear program, adding it would be a bumpy road to a summit between leaders of the United States and the Democratic People's Republic of Korea.

Mattis made the remarks on Sunday at the 17th Asia Security Summit, commonly known as the Shangri-La Dialogue, which opened in Singapore on Friday.

"We can anticipate, at best, a bumpy road to the negotiations," Mattis said. "In this moment we are steadfastly committed to strengthening even further our defense cooperation as the best means for preserving the peace."

Plans are moving forward as US President Donald Trump confirmed his meeting with DPRK top leader Kim Jong-un will be held on June 12 in Singapore as originally scheduled. And Mattis repeated the US position that the DPRK will only receive relief from UN national security sanctions when it demonstrates "verifiable and irreversible steps" to denuclearization.

Mattis's remark shows that Washington's attitude on the denuclearization has never changed, which is different from Pyongyang's understanding in the same issue, said Ruan Zongze, deputy head and senior fellow at the China Institute of International Studies.

Ruan said that to have an agreement on the concept of denuclearization is still seen as a major obstacle for the two sides to reach a deal in the summit.

On Friday, Trump met the visiting vice-chairman of the DPRK's Workers' Party of Korea Central Committee Kim Yong-chol for two hours. Trump told reporters at the White House that his meeting with Kim Jong-un is back on after receiving a personal letter from the DPRK leader.

Foreign Ministry spokeswoman Hua Chunying on Saturday said that the Chinese side hopes and supports the DPRK and the US in actively pushing forward preparations for the summit, reiterating that the current situation on the Korean Peninsula is at a rare historical juncture and the summit is crucial to denuclearization and lasting peace on the peninsula.

The Republic of Korea's presidential office also welcomed Trump's decision to revive the summit.

The key thing is "to establish a mechanism that can maintain the momentum of dialogue for a long run", Ruan said. He said China had long urged direct dialogue between the DPRK and US.

"What relevant parties are doing to ease tensions on the peninsula is actually in line with China's proposals", Ruan said.

Contact the writer at?panmengqi@chinadaily.com.cn