North Korea on Friday accused the United States of hypocrisy for remaining silent over a South Korean missile test while condemning Pyongyang's recent launches.

"The US double-dealing attitude and despicable mode of action has been brought to light," a spokesman for the North's powerful National Defence Commission (NDC) said in a statement.

The statement, carried by the North's official KCNA news agency, comes at a time of elevated military tensions, with Pyongyang threatening a "new" type of nuclear test.

"As long as the US persists in its hostile policy... according to its high-handed, arbitrary and gangster-like double standards, (North Korea) will push ahead with countermeasures for self-defence to put an end to the policy," the spokesman said.

His remarks were triggered by South Korea's test-firing last month of a new ballistic missile capable of carrying a one-tonne payload to any part of North Korea.

The missile was developed under an agreement reached in 2012 with the United States to almost triple the range of the South's ballistic missile systems.

The NDC spokesman said the silence that greeted the South Korean launch was in sharp contrast to the US and UN condemnation of the North's recent test of two medium-range ballistic missiles.

UN Security Council resolutions prohibit any ballistic missile tests by North Korea.

"If the ballistic missile launched by the South Korean puppet forces is not problematic, the (North's) launch of satellites or rockets should be no problem either," the spokesman said.

North Korea successfully put a satellite into orbit in December 2012 on a rocket that Pyongyang said was designed for purely scientific missions.

The international community said it was a disguised ballistic missile test and the UN Security Council tightened existing sanctions as a result.

S.Korea, US launch largest-ever air drill
Seoul (AFP) April 11, 2014 - South Korea and the United States kicked off their largest-ever joint air drill on Friday at a time of elevated military tensions with North Korea.

The so-called "Max Thunder" exercise, which is held twice a year, will last until April 25 and involve 103 aircraft and 1,400 service personnel, a South Korean air force spokesman said.

"In numerical terms, it's the largest exercise of its kind that we've done," the spokesman told AFP.

The last Max Thunder drill held in October-November last year involved 97 aircraft and some 1,000 troops.

Seoul's F-15K jet fighters will take part along with US Air Force F-15 and F-16s and US Marines' FA-18 and EA-18 aircraft.

"The combined air forces will strengthen their battle readiness under the current situation when tension rises over the Korean peninsula," a South Korean air force statement said.

The exercise will focus on "practical scenarios" involving precision attacks on enemy positions and supply-drop missions for troops infiltrating enemy territory.

It comes as the allies are winding up separate annual military drills which began late February, and have been denounced by Pyongyang as rehearsals for invasion.

In a pointed protest at the exercises, Pyongyang carried out a series of rocket and missile launches, capped by its first mid-range missile test since 2009 on March 26.

The two Koreas also traded artillery fire across the tense Yellow Sea border on March 31, after the North dropped around 100 shells across the maritime boundary during a live-fire drill.

The exchange followed a North Korean warning that it might carry out a "new" form of nuclear test -- a possible reference to a uranium-based device or a miniaturised warhead small enough to fit on a ballistic missile.

The United States, South Korea and Japan, meeting in Washington on Monday, condemned the ballistic missile tests and urged the North "to refrain from further threatening actions".