SEOUL, Korea, Republic Of - North Korea is believed to have placed a new, powerful midrange missile on standby for an impending launch, a news report said Tuesday.

The reported launch plans came two days after North Korea said it successfully test-fired a ballistic missile from a submarine in a continuation of its weapons tests amid ongoing South Korea-U.S. military drills. Seoul officials said they could not confirm whether Sunday's test-firing was a success.

South Korea's Yonhap news agency cited an unidentified Seoul official as saying Tuesday that the country's military had unspecified evidence indicating North Korea would likely soon launch a midrange Musudan missile.

Seoul's Defence Ministry said it had no such intelligence. South Korean officials often refuse to discuss North Korea's weapons systems publicly because they involve confidential military intelligence.

Yonhap said the missile on standby is one of two Musudan missiles North Korea had earlier deployed in the northeast before it fired one earlier this month.

South Korean and U.S. officials said there was a North Korean missile launch on April 15, the birthday of the North's late founder, Kim Il Sung, but they have not officially confirmed it was a Musudan firing. U.S. officials said the earlier launch ended in failure.

A Musudan has a reach of 3,500 kilometres, putting far-off U.S. military installments in Asia in range.

North Korea typically conducts more weapons tests when South Korean and U.S. troops conduct annual springtime drills that Pyongyang views as an invasion rehearsal. This year's drills end later this week.

Last week, South Korea's president said there were signs that North Korea was preparing for a fifth nuclear bomb test amid media reports of increased activity at the country's main nuclear test site. North Korea carried out a fourth nuclear test in January.

Analysts say a new atomic test could happen before North Korea holds a ruling Workers' Party congress in early May so that leader Kim Jong Un can burnish his image at home and further cement his grip on power.