Seoul reportedly plans to announce its agreement with Washington on revising a bilateral ballistic missile pact as early as Sunday. 

The revision is to allow South Korea to develop ballistic missiles with a range of up to 800 km, up from the previous 300 km, so as to better deal with missile threats from North Korea, reports say. The weight of the payload is to remain at the current 500 kg. 

“(Seoul) is considering announcing the agreement as early as tomorrow (on Sunday) or early next week,” a high-level official told media. 

The announcement is expected to be made at the presidential office of Cheong Wa Dae which has led the negotiations with the U.S. 

Since early last year, the two sides have been engaged in official negotiations over amending the pact signed in 1979 and revised in 2001. 

Washington has apparently been reluctant to alter the pact as it could undermine its initiatives of non-proliferation and arms control, and could provoke neighboring states such as China, Russia and Japan, not to mention the North. 

The revision is also expected to ease the limits of the range and payload, which the bilateral pact has imposed on Seoul’s acquisition of unmanned aerial vehicles. The payload weight is rumored to increase to more than 2,000 tons. 

With an aim to deploy them in 2021, the South Korean military has recently launched a 500 billion won ($447 million) project to indigenously develop an unmanned combat aerial vehicle. 

It has also sought to acquire an unmanned surveillance plane such as the Global Hawk spy drone so as to enhance intelligence capabilities to better monitor North Korean military movements, ahead of Seoul’s retaking of wartime operational control from Washington in December 2015. 

As Pyongyang has continued to test its increasingly sophisticated missiles under the disguise of satellite launches, Seoul has long demanded that the range be extended to longer than 1000 km to put all core military targets in the North within striking range.

In April, the communist state launched a long-range missile, claiming again that the launch aimed to put a scientific satellite into orbit. Experts say that it was a test of the Taepodong-2 missile, the longest-range North Korean missile under development. 

The Taepodong-2 missile is presumed to have a range of more than 6,700 km, enough to hit parts of Alaska, but still short of reaching the U.S. mainland. The missile’s tests have so far failed. 

The longest-range North Korean ballistic missile, deployed since 2007, is the Musudan missile with a range of 3,000-4,000 km. This missile, in theory, brings Guam, a key U.S. strategic base in the Asia-Pacific region, within its range.