North Korean leader Kim Jong-Un has hailed the firing of a new anti-ship rocket as "another fresh milestone" in bolstering the country's naval power following the testing of a submarine-launched ballistic missile (SLBM).

Kim watched the test of the "highly intelligent" rockets to be deployed at naval units, Pyongyang's KCNA news agency reported on Monday.

He "noted with great pleasure that it marked another fresh milestone in bolstering up the Juche (self-reliance)-based naval force", it said.

"Ultra-modern strike means of Korean style have been studied and developed one after another recently to completely contain the hostile forces," Kim was quoted as saying.

The South's defence ministry said the North had tested three short-range missiles with a range of nearly 100 kilometres (62 miles) Sunday off its east coast.

"North Korea appears to be developing new missiles that would replace its old Soviet-designed anti-ship missiles," ministry spokesman Kim Min-Seok told reporters.

The test was the latest since Pyongyang claimed on May 9 it had successfully test-fired an SLBM -- a technology that could eventually offer the nuclear-armed state a survivable second-strike capability.

A fully developed SLBM capability would take the North Korean nuclear threat to a new level, allowing deployment far beyond the Korean peninsula.

But some experts have questioned the authenticity of the May test, saying photos of the launch might have been digitally manipulated.

N. Korea soldier defects across land border
Seoul (AFP) June 15, 2015 - A young North Korean soldier walked into South Korea Monday in a rare defection through one of the world's most fortified frontiers, saying he deserted his camp because of habitual beating, military officials said.

The 19-year-old soldier surrendered himself to South Korean border guards around 8:00 am (2300 GMT) after crossing the frontier in Hwacheon, northeast of Seoul, the South's defence ministry said.

"We've confirmed his will to defect after he reached our guard post," a ministry spokesman told AFP.

The North Korean soldier told investigators that he had decided to defect "because of habitual beating at his camp while harbouring complaints about the reality of his homeland", the spokesman added.

The defection sparked a tense stand-off between North and South Korean border guards across the four-kilometre- (2.5-mile-) wide and 248-kilometre-long demilitarised zone (DMZ), but there was no conflict, the Yonhap news agency reported.

The man identified himself as a private, the lowest rank among the North's enlistees, it said.

Hundreds of North Koreans flee their isolated homeland each year but it is rare for defectors to cross the land border, marked by barbed wire and guarded by tens of thousands of troops on both sides.

Despite its name, the DMZ separating the two Koreas, which remain technically at war, is one of the world's most heavily militarised frontiers, bristling with watchtowers and landmines.

Most North Koreans who flee repression and poverty at home cross the porous frontier with China first before travelling through a Southeast Asian nation and eventually arriving in South Korea.

In 2012, a North Korean soldier walked unchecked through rows of electrified fencing and surveillance cameras, prompting Seoul to sack three field commanders for a security lapse.

In August last year, two North Koreans swam across the Yellow Sea border to a South Korean frontline island.

So far about 28,000 North Koreans have resettled in the South since the end of the 1950-53 Korean War, mostly after the great famine in the 1990s.

But the number of escapees has decreased sharply since North Korean leader Kim Jong-Un took power following the death of his father in late 2011.

Under Kim, the isolated state has tightened border security, while China has launched a crackdown on North Korean escapees on its side of the border.

China -- the North's sole major ally -- typically considers them illegal economic migrants and repatriates them despite criticisms from human rights groups.

Many face severe punishment including, rights monitors say, torture and a term in a prison camp once they are sent back to the North.