South Korea and the United States are close to agreement on expanding the range of Seoul's ballistic missiles to better guard against threats from North Korea, a report said Thursday.

Defence Minister Kim Kwan-Jin, in an interview with the Segye Times, said he would try to agree an increase by the end of this year on the current 300-kilometre (186-mile) limit.

"The US has agreed on the need for us to strengthen ballistic missile capability in order to better respond to North Korea's ballistic missile threat," the paper quoted Kim as saying.

"One thing I can say for sure is that the range will be improved compared to now."

The US stations 28,500 troops in South Korea, a close ally, and guarantees a nuclear "umbrella" in case of any atomic attack. In return, Seoul accepts limits on its missile capabilities.

President Lee Myung-Bak said in March the North's missiles could reach the southern island of Jeju, more than 400 kilometres south of the border, and stressed that Seoul needed a "realistic adjustment" to its own missile range.

The need to strengthen Seoul's missile capability took on new urgency after the North's latest long-range rocket launch in April.

Pyongyang claimed its aim was only to put a satellite into orbit but the US and allies saw it as a disguised long-range missile test banned under UN resolutions.

The South believes the North has 1,000 missiles of various types, many of them targeted at Seoul or other locations in the South.