The focus of the negotiations is expected to be on doubling the payload weight limit to 1 ton, a source said, declining to be named.

"During the summit between the allies' leaders, there was a discussion regarding the payload part (in the guideline), and (the negotiations) will be in line with that," Yoon said.

"It is fair to say that more weight will be given to the payload part rather than the missile range issue," he added, noting the negotiations would open "at the earliest date."

A senior presidential official said that there has yet to be any concrete consultations with Washington over how much the payload weight limit needs to be increased.

"Given the U.S. shares (the need) for increasing the warhead weight, the heavier the better," the official told reporters on condition of anonymity.

Asked whether there were prior consultations with Beijing and Tokyo over the issue, he said, "There is no need for us to definitely inform them of it in advance ... We will do if need be."

The revision has been a source of controversy as opponents here argue that it could provoke neighboring countries, including China and Russia. But Seoul asserted the need for it based on national security grounds.

The guideline was first signed in 1979 and revised in 2001 and then 2012. (Yonhap)