Chun Yung-woo, the chief national security adviser for President Lee Myung-bak, told a news conference the U.S. government had agreed to easing restrictions on South Korea's missile capabilities the two countries first agreed to in 1979, The New York Times reported.
Chun said the range of missiles had been extended to about 500 miles from 190, which would put all of North Korea in range, but not China or Japan.
The revisions also allow Seoul to increase the munitions payload of missiles and drone aircraft, the Yonhap news agency said.
"The most important purpose our government placed on revising the missile guideline lies in deterring armed provocations by North Korea," Chun told the news conference.
Western intelligence officials widely believe North Korea has at stockpiled at least 1,000 cruise and ballistic missiles, some of them with long-range capabilities.