North Korea on Wednesday accused the United States of pushing the Korean Peninsula to "the point of explosion" after it dispatched two huge bombers in a show of force against Pyongyang.

The supersonic B-1B Lancers flew over South Korea Tuesday as Washington vowed its "unshakeable commitment" to defend its allies in the region following North Korea's fifth and largest-ever nuclear test conducted last week.

Washington called the demonstration "just one example of the full range of military capabilities". It took similar military actions following previous atomic tests.

North Korea labelled the flyover by the "infamous" nuclear bombers as Washington's attempt to seek "an opportunity of mounting a preemptive nuclear attack," referring to US plans to deploy further strategic assets to the peninsula.

"These extremely reckless provocations of the US imperialist warmongers are pushing the situation on the Korean peninsula to the point of explosion hour by hour," the state-run KCNA news agency said.

It warned that the North Korean army was fully armed with "all means for military counteraction" to strike back at any enemy attack in "a single blow".

Washington is planning to send the nuclear-powered aircraft carrier the USS Ronald Reagan and the Japan-based Carrier Strike Group Five to South Korean waters next month for a joint naval exercise, according to South Korea's Yonhap news agency.

A spokesman for United States Forces Korea declined to confirm the report to AFP, citing operational matters.

South Korea hosts 28,000 US troops as the two Koreas technically remain at war since the 1950-53 Korean War ended in an armistice instead of a peace treaty.

The bombers' flight came after the North on Friday carried out what it described as a "nuclear warhead test" and vowed to take further measures to increase its nuclear strike force "in quality and in quantity".

Activists launch leaflets into N. Korea after nuclear test
Seoul (AFP) Sept 15, 2016 - South Korean activists launched tens of thousands of anti-Pyongyang leaflets across the border into North Korea on Thursday, denouncing its latest nuclear test and defying threats of retaliation.

The leaflets, criticising leader Kim Jong-Un for putting nuclear weapons before the wellbeing of his people, were launched with helium balloons from the border city of Paju.

The propaganda exercise, organised by North Korean defector-turned-activist Park Sang-Hak, came amid surging military tensions on the divided Korean peninsula following the North's fifth and largest-ever nuclear test last week.

Hours before the balloon launch was scheduled to begin, the North's official KCNA news agency published a commentary describing Park as "human scum without an equal in the world."

KCNA said the balloon launch was a desperate response to the success of last week's test, and a bid by Seoul to "stoke confrontation" over the holiday period.

The launch came in the middle of the three-day Chuseok harvest festival holiday -- celebrated on both sides of the border.

Conservative South Korean activists, including many North Korean defectors, have been carrying out leafleting exercises using giant helium balloons for years -- a practice that infuriates Pyongyang which has threatened military strikes in response.

Park Sang-Hak said strong winds at the border had restricted Thursday's event to the launch of around 150,000 leaflets -- half the planned number.

"We are doing this to inform the 20 million starving people in North Korea of the truth," Park told AFP.

"At this moment, when hundreds of thousands of people are suffering from terrible floods, Kim Jong-Un conducted another nuclear test.

"So, who is calling who 'human scum?'" he said.

North Korean state media has described ongoing floods as the worst to hit the country since World War II.

According to a UN agency report, 138 people have died and 400 are missing after torrential rains caused devastation in the country's far north.