SEOUL/WASHINGTON (REUTERS) - United States President Donald Trump said on Wednesday (Oct 10) that South Korea will not lift sanctions on Pyongyang without US approval, after the South Korean foreign minister softened earlier comments that some of its unilateral sanctions were under review.

Mr Trump's rejection of South Korea easing sanctions alone outlines the official position of the US and South Korea - that the two countries remain in lockstep on North Korea.

He has encouraged US allies to maintain sanctions on North Korea until it denuclearises as part of his administration's "maximum pressure" campaign against Pyongyang.

Asked about reports that South Korea was considering lifting some sanctions against North Korea, Mr Trump said: "They won't do it without our approval. They do nothing without our approval."

South Korean foreign minister Kang Kyung-wha suggested during a parliamentary audit on Wednesday that Seoul was considering easing its own sanctions against the North to encourage its denuclearisation.

South Korea imposed unilateral sanctions on the North in 2010 following an attack on a warship that killed 45 South Korean sailors, banning most bilateral trade and exchanges.

Dr Kang later walked back her comments after they sparked criticism from some conservative lawmakers, claiming North Korea should first apologise for the attack.

The South Korean foreign ministry also officially denied that the government was reviewing the matter.

However, there are growing calls for easing sanctions.

China, Russia and North Korea believe it is necessary to consider adjusting United Nations sanctions against Pyongyang at an appropriate time, China's foreign ministry said on Wednesday.

In a rare confirmation of discord between Seoul and Washington, Dr Kang also said on Wednesday that US Secretary of State Mike Pompeo had expressed "discontent" with an inter-Korean military pact reached during a summit last month.

She said there were views in the US regarding "adjusting the pace" of inter-Korean moves.

The drive for denuclearisation sprang from pledges made by Mr Trump and North Korean leader Kim Jong Un at their historic summit in Singapore in June, although there has since been disagreement over how that would be achieved.

Mr Trump said on Tuesday that his second summit with Mr Kim would be held after US congressional elections on Nov 6.

Speaking to reporters as he flew to Iowa for a political rally, Mr Trump said: "It'll be after the midterms. I just can't leave now."

Earlier on Tuesday, Mr Trump told reporters that plans were being made for his second summit with Mr Kim and that he thought "incredible" progress had been made in US talks with the long-isolated North Asian country.

The North has claimed that the US should provide "corresponding" measures in response to its practical steps for denuclearisation, reported Yonhap.

It has called for a formal end to the 1950-53 Korean War - which was halted with a truce, not a peace treaty - and the lifting of sanctions imposed on its regime. China and Russia have been supportive of Pyongyang's demands.

The US remains firm that no sanctions relief will come until the North completely gives up its nuclear weapons programme.

Mr Trump noted on Tuesday that the US had not lifted the "very big sanctions" it has imposed on Pyongyang.

"I'd love to remove them, but we have to get something for doing it," he said.

Senior diplomats of North Korea, China and Russia said denuclearisation should be carried out in a "stage-by-stage and simultaneous way" and emphasised the importance of confidence-building in the process.