SEOUL: South Korea never considered lifting sanctions against North Korea imposed over the 2010 sinking of a South Korean warship, the country's Unification Minister Cho Myoung-gyon said on Thursday.

South Korea's Foreign Minister Kang Kyung-wha said on Wednesday that the sanctions, imposed against Pyongyang following a torpedo attack on a corvette that killed 46 South Korean sailors in 2010, were under review.

North Korea has denied any involvement in the sinking.

Kang's remarks on sanctions, retracted after criticism from South Korean lawmakers, prompted U.S. President Donald Trump to say South Korea would need US approval to relieve sanctions.

"They won't do it without our approval. They do nothing without our approval," Trump told reporters, when asked about her comments.

Trump has said sanctions will remain in place until North Korea it denuclearises.

Kang backtracked on her remarks after facing criticism from some conservative lawmakers that the sanctions cannot be removed unless North Korea first apologised for the attack, a stance adopted by former South Korean governments.

The sanctions ban all North Korean ships entering South Korean ports and cut off most inter-Korean exchanges, including tourism, trade and aid.

"There will need to be action regarding the issue of the Cheonan warship, which was the cause (of the sanctions)," Cho said during a parliamentary audit.

Trump's comments triggered heated debate in South Korea, with some conservative lawmakers calling them an "insult".

"'Approval' is a strong and insulting word meant to say that we are progressing too fast with the North without seeking consensus with the United States," said Kim Jae-kyung from a conservative opposition party.

South Korean President Moon Jae-in has pursued a thaw in cross-border ties, holding three summits with North Korean leader Kim Jong Un this year. Last month's third summit in Pyongyang was partly aimed at salvaging faltering nuclear talks between the North and the United States.

At their latest meeting, Moon and Kim agreed to resume economic cooperation, with construction work to be started within this year to reconnect rail and road links. They also agreed to reopen a joint factory park in the North's border city of Kaesong and the Mount Kumgang tours, when conditions are met.

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

Cho refused to comment on Trump's remarks, but said Washington was not opposed to inter-Korean dialogue and exchanges, and the allies are in close consultation.

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