North Korea yesterday threatened a "physical response" to US-South Korean naval exercises this weekend after the US accused Pyongyang of waging a "campaign" of provocation.

Diplomatic sparks flew as US Secretary of State Hillary Clinton and North Korean Foreign Minister Pak Ui-Chun attended an Asia-Pacific security forum amid escalating tensions on the Korean peninsula.

"There will be a physical response against the steps imposed by the US militarily.

"It is no longer the 19th century... gunboat diplomacy," North Korean delegation spokesman Ri Tong Il told reporters in Hanoi.

The naval drills - involving a US aircraft carrier, destroyers, fighter aircraft and thousands of troops - were a "grave threat to the Korean peninsula, and also the region of Asia as a whole", he added.

"It is against the sovereignty of the DPRK (North Korea) and the security of the DPRK," he said.

The US and South Korea had hoped the Asian Regional Forum (ARF) would condemn North Korea over the sinking of a South Korean warship in March, diplomats said, but a statement only expressed "deep concern".

"Here in Asia, an isolated and belligerent North Korea has embarked on a campaign of provocative, dangerous behaviour," Mrs Clinton said in prepared remarks to foreign ministers gathered at the region's biggest security dialogue.