Image copyright KCNA / EPA Image caption North Korea is thought to have used the Musudan missile, pictured here in a 2010 file photo, in the failed launch

North Korea has test fired a mid-range ballistic missile which crashed a few seconds after launch, say South Korean military officials.

It is thought to be the second test of the North's new Musudan missile. An attempt earlier this month also failed.

The tests come amid a recent ramp-up in weapons activity as the country prepares for a rare party congress.

Reports suggest it is planning a fifth nuclear test, despite condemnation of its last test in January.

South Korean officials said the mid-range missile launch took place early Thursday morning near the eastern coastal city of Wonsan but the missile "crashed a few seconds later" in the coastal area, reported Yonhap news agency.

The incident was captured by a US surveillance satellite.

The Musudan missiles are said to be able to travel up to 4,000km (2,485 miles), within the range of US territories in the Pacific.

Stephen Evans, BBC News, Korea Correspondent

Image copyright KCNA Image caption Eye on the prize: Kim Jong-un is believed to be ramping up weapons activity for next week's party congress

No confirmation of the attempt or the failure has come from North Korea, but sources in South Korea say that the movement of two so-called Musudan missiles, mounted on trucks, was detected earlier in the month.

One was launched two weeks ago and tracked but failed to go far. The same has now happened to the second, according to South Korea.

Kim Jong-un is building up to a big event in just over a week, a rare meeting of the ruling Workers' Party in Pyongyang.

He has trumpeted a series of announcements about progress towards having a nuclear-tipped missile capable of striking Washington. Failed launches indicate that the reality may not match the rhetoric.

All the same, they indicate determination. A fifth nuclear test coinciding with the congress would not be a surprise.

On Saturday, North Korea's foreign minister Ri Yong-su suggested that it would suspend nuclear tests if the US ended its annual military exercises with the South.

But US President Barack Obama dismissed the proposal, saying it was not serious and that North Korea would "have to do better than that".

Image copyright KCNA Image caption North Korea released a picture on Sunday of an alleged submarine missile test

Strengthened international sanctions were placed on North Korea after it tested what it claimed was a hydrogen bomb and launched a long-range missile.

Over the weekend it also claimed it fired a submarine ballistic missile.

Observers have speculated that Pyongyang is boosting the development of its weapons programs ahead of its political conference aimed at solidifying the power of its leader Kim Jong-un.

The North announced this week that the congress, which was last held in 1980, would take place on 6 May.