North Korea warned Tuesday that any accidental clash during an upcoming US-South Korea naval exercise could spark war, as tensions remained high over the sinking of a South Korean warship.

Minju Josun, the cabinet's official daily, accused the South and its US ally of "fabricating" facts about the sinking to incite a war against the communist state.

"It is as clear as day that a small accident that might occur during the joint military exercise would easily spread to an armed clash and eventually, to an all-out war," it said, slamming the planned drill as provocative and dangerous.

The United States and South Korea are planning a special naval exercise as a show of strength in response to the sinking, which they blame on the North. No dates have been announced.

"If the US imperialists, gripped by their pipe dream of invading the North, ignite a new war on the Korean peninsula, our military and the people will wipe out not only the invaders but their strongholds as well and achieve a final triumph," the daily said.

Beijing last week expressed concern at the planned joint exercise, which reportedly will include a nuclear-powered US aircraft carrier battle group in close proximity to China's territorial waters.

China will start six days of live-fire military exercises off its east coast later this week, state press reported Tuesday.

South Korea, citing the findings of a multinational investigation, last month accused its neighbour of sinking the Cheonan corvette near the disputed border in March with the loss of 46 lives.

The South announced its own reprisals and also wants the United Nations Security Council to censure the North. The North has denied involvement and threatened a military response to any UN action.

On Monday it vowed to strengthen its nuclear weaponry in an unspecified "newly developed way" in the face of what it termed US hostility.

The same day Pyongyang's military accused the United States of bringing unspecified heavy weapons into the border truce village of Panmunjom.

It warned of "strong military countermeasures" at the village, a top tourist attraction for visitors from the South, unless they are withdrawn.

The US-led United Nations Command Tuesday denied any heavy weapons had been introduced and said it continues to abide by the armistice agreement that ended the 1950-53 war.

China has not backed any UN condemnation of the North and has not publicly accused its ally of being behind the warship sinking.

US President Barack Obama, in weekend comments at a G20 meeting in Canada, accused China of turning a blind eye to its ally's actions -- a claim rejected by Beijing.

"We don't favour either side and we decide our position on the merits of the issue. China's position and efforts on this issue brook no accusations," foreign ministry spokesman Qin Gang said Tuesday when asked about Obama's comments.

"We don't do anything to fan the flames."

Pyongyang on Tuesday hit back at a communique issued last week by the G8, a grouping of rich countries that does not include China, in which leaders called for "appropriate measures to be taken against those reponsible for the attack" on the warship.

In a statement carried by the official Korean Central News Agency, a North Korean spokesman said the G8 was "heading for a cemetery of history as it has been reduced to an evil group blindly conniving and defending its allies, far from taking principle and truth as a standard."

South Korea based its case against the North partly on a section of torpedo salvaged from the bed of the Yellow Sea, where the warship went down. Investigators said this matched blueprints of North Korean torpedoes.

But military investigators quoted by Yonhap news agency admitted Tuesday they mistakenly showed the wrong blueprint at a nationally televised news conference last month.

They were quoted as saying that the blueprint shown at the news conference was of a PT-97W torpedo, not the CHT-02D midget torpedo that sank the Cheonan.

The investigators called the incident a "mistake by a working-level staff member".

The South meanwhile marked the anniversary of a 2002 naval clash near the Yellow Sea border, paying tribute to six of its sailors who died. An estimated 13 North Koreans were killed.

At a ceremony Prime Minister Chung Un-Chan also demanded that the North apologise for the sinking of the Cheonan.