China wants to ease tensions on the Korean peninsula and was surprised and concerned when its ally Pyongyang abruptly shut the door on dialogue with Seoul, a senior US official said Friday.

Kurt Campbell, Assistant Secretary of State for East Asian and Pacific affairs, was speaking in South Korea at the end of an Asian tour which also took him to China, Mongolia and Indonesia.

North Korea announced on May 30 it would no longer have dealings with the South's conservative government, further raising tensions.

Two days afterwards, it disclosed apparent secret approaches from Seoul for summit talks and poured scorn on them.

Last Friday the North's military threatened retaliation unless Seoul punishes troops who used pictures of Pyongyang's ruling dynasty as rifle-range targets. The practice has been halted.

"In all of our meetings (in Beijing), we urged China to make best efforts to encourage North Korea to improve relations with South Korea," Campbell told journalists after talks with Foreign Minister Kim Sung-Hwan and deputy minister Kim Jae-Shin.

Campbell said China, the United States and South Korea all agree there must be an improvement in such relations, "and I think China wants to take efforts to help support that process".

Relations have been icy since the South accused the North of sinking one of its warships in March 2010 with the loss of 46 lives.

The North denies involvement in the sinking. But it shelled a South Korean border island last November, killing four people including two civilians.

It says the shelling was provoked by its neighbour and refuses to apologise for either incident -- a precondition set by Seoul before any serious dialogue.

Campbell said the Chinese were "concerned" by the disruption in inter-Korean talks and "a little surprised."

Chinese officials "very much want to see improvement in dialogue between the North and South and we encourage that process as well", he said.

The North's leader Kim Il-Sung apparently did not inform his hosts of the upcoming rupture in cross-border ties when he visited Beijing last month, Campbell said.

"I don't think the North Koreans gave an indication that they were about to so abruptly and so publicly break contact with South Korea," he said.

"We expressed our concerns and I think all of our Chinese interlocutors indicated they had no knowledge in advance that such steps were being contemplated."

In response to a question, the assistant secretary said the United States is still reviewing North Korea's need for food aid after a recent assessment visit by a US team.

"We did very closely communicate to South Korean friends that no decision has been taken and under any circumstances, we will coordinate in advance with South Korea," he added.

South Korea opposes any resumption of US food aid at this time.

Some Seoul officials say the North is exaggerating its woes in hopes of winning food aid, possibly to distribute during mass celebrations next year marking the 100th birth anniversary of the regime's founder Kim Il-Sung.