North Korea has said it will suspend its nuclear tests if the US stops its annual military exercises with South Korea.

Foreign minister Ri Su-yong also told the Associated Press news agency that his country would not be cowed by international sanctions.

A US official has defended the drills as a sign of commitment to South Korea.

Meanwhile, Pyongyang said Saturday's submarine-launched ballistic missile test was a "great success".

"It fully confirmed and reinforced the reliability of the Korean-style underwater launching system and perfectly met all technical requirements for carrying out... underwater attack operation," the North Korean news agency KCNA said.

It added that the test gave the country "one more means for powerful nuclear attack".

North Korea is banned from nuclear tests and activities that use ballistic missile technology under UN sanctions dating back to 2006.

Earlier, Ri Su-yong defended his country's right to have a nuclear deterrent and said the US drove North Korea to develop such weapons as an act of self-defence.

He suggested that the suspension of the military drills could open the door to talks and reduced tensions.

"If we continue on this path of confrontation, this will lead to very catastrophic results, not only for the two countries but for the whole entire world as well," he told AP.

"Stop the nuclear war exercises in the Korean Peninsula, then we should also cease our nuclear tests."

It was a rare interview by a top North Korean official with a foreign media outlet. The conversation took place in the country's diplomatic mission at the UN, the agency said.

An unnamed US official quoted by AP defended the drills in South Korea as demonstrating Washington's commitment to its alliance with Seoul.

The US has insisted the North give up its nuclear weapons programme first before any negotiations and has ignored similar proposals in the past, according to the agency.

Ri Su-yong also said sanctions would not sway his country: "If they believe they can actually frustrate us with sanctions, they are totally mistaken.

"The more pressure you put on to something, the more emotionally you react to stand up against it. And this is important for the American policymakers to be aware of."

'Hitting the puppet forces'

The interview came hours after North Korea said it launched a ballistic missile from a submarine, a type of missile hard to detect.

Some experts, however, think the North has fired missiles from submerged platforms, rather than from submarines.

The North's official news agency also said the country's leader Kim Jong-un observed from a test facility as the ballistic missile surged from a submarine and spewed out a "massive stream of flames'' as it soared into the sky.

It said the missile met all technical thresholds, but did not specify where the test took place.

South Korean officials, however, said the launch took place near the eastern coastal town of Sinpo.

The report also quoted Kim Jong Un as saying that the North was now capable of "hitting the heads of the South Korean puppet forces and the US imperialists anytime as it pleases".

North Korea has so far conducted four nuclear tests-the first one in October 2006 and the latest in January this year.

The UN Security Council responded to the latter by imposing its strongest sanctions to date over the North's nuclear weapons programme.

Last month North Korea said it had developed nuclear warheads small enough to fit on ballistic missiles, although experts cast doubt on the claims.

Analysts believe the North may be gearing up for a fifth test as a show of strength ahead of the North Korean Workers' Party Congress in early May, the first such meeting since 1980.