The United States said on Sunday that North Korea will get relief from United Nations sanctions only after it takes clear and irreversible steps towards denuclearisation, Reuters reported.

“We will continue to implement all UN Security Council resolutions on North Korea,” Defense Secretary James Mattis said in Singapore. “North Korea will receive relief only when it demonstrates verifiable and irreversible steps to denuclearisation.”

He said: “We can anticipate, at best, a bumpy road to the [negotiations].” Mattis was speaking at the Shangri-La dialogue.

After much dilly-dally, President Donald Trump had on Friday said his summit with North Korean leader Kim Jong-un in Singapore will be held as scheduled on June 12.

Mattis’ Japanese counterpart Itsunori Onodera said that while the solution to the North Korean nuclear crisis must be diplomatic, the defence cooperation among the United States and its Asian allies was key to bringing it about.

“Japan, [South] Korea and the US continue to agree that pressure is needed to be applied on North Korea,” Onodera told reporters.

Both the US and North Korea have oscillated over holding the summit. On May 24, Trump called off the summit, blaming Pyongyang’s “tremendous anger” and “open hostility”. This came hours after North Korea announced it had dismantled its nuclear bomb test site in Punngye-ri. A day later, North Korea said it was still open to resolving problems with the US “at any time in any way”.

Trump then said his administration was in talks with North Korea and hinted that the summit may go ahead as planned. Kim Jong-un has also expressed his “fixed will” that the summit should go ahead.