South Korea and the United States have been in talks to revise a bilateral pact that could allow for Seoul's bid to make missiles capable of landing anywhere in North Korea.

The revelation was made by a state agency report citing government sources.

The move comes amid swelling calls to increase the country's missile capability to counter North Korean missile threats.

It also comes on the heels of remarks by U.S. Defense Secretary Robert Gates expressing serious concerns over North Korea's intercontinental ballistic missile program.

South Korea and the United States stage regular exercises with their combined forces. But the recent drills have come in the wake of North Korea shelling a South Korean island and the sinking of a South Korean warship in which 46 sailors were killed. Pyongyang is suspected to have been responsible for the sinking.

Under a 2001 agreement with the United States, South Korea restricts its missile capability to a range of about 186 miles and a payload of around 200 pounds to meet guideline of the Missile Technology Control Regime.

As the regime only applies to high-velocity, free-flight ballistic missiles, the South Korean military has instead deployed slower, surface-skimming cruise missiles with ranges of between 620 to more than 800 miles.

"As the talks are still at an early stage, it is too early to say how long the missile range could be extended," the Seoul government source was quoted saying in a report the South Korean News Agency. "But there is a need to extend it beyond 1,000 kilometers (621 miles)."

It is understood that North Korea has developed intermediate-range missiles capable of traveling up to 1,800 miles.

An estimated 28,500 U.S. troops are based in South Korea to deter potential aggression from North Korea.

Although the Korean War ended in 1953, the countries haven't signed a peace agreement, remaining divided by one of the world's most fortified borders.

Relations between North and South have soured since the sinking of the warship late last year.

During a five-day tour to South Korea, China and Japan last week, Gates said North Korea was becoming a direct threat to the United States, forecasting that the North was on the way to developing intercontinental ballistic missiles within five years.

"I think that North Korea will have developed an intercontinental ballistic missile within that time frame," Gates told reporters. But he said he doubted if the North will be able to field many ICBMs, saying, "I believe they will have a very limited capability."

U.S. officials are cautious about the missile talks because they may spark a backlash from China and Japan and North Korea, also.

North Korea is believed to have more than 600 Scud missiles with a range of 200 to 310 miles and 200 Rodongs with a range of 800 miles.