North Korea has almost completed modifications to its long-range rocket launch facility near the border with China, government sources here said Wednesday.
  

A new 67-meter-tall gantry has been spotted in the Dongchang-ri site, which the North calls the Sohae Satellite Launching Station, a source said apparently on the basis of satellite imagery.
  

"We believe that the North will use the extended gantry in Dongchang-ri to fire a long-range missile longer than the Unha-3," the source said. "We think (the North) will carry out a provocation around the 70th anniversary of the founding of the Workers' Party on Oct. 10."
  

South Korea's Defense Minister Han Min-koo earlier said the North is expected to take "strategically provocative action" around the anniversary.
  

"Our military is closely watching and monitoring movements related to North Korea's missile launches, including the construction activity at the Dongchang-ri missile launch site," Defense Ministry spokesman Kim Min-seok said.
  

The secretive communist nation began work in late 2013 on the new structure.
  

Military and intelligence officials said they believe the upgraded facility can be used for the launch of long-range missiles twice the size of the 30-meter-long Unha-3, which put a satellite into orbit in December 2012.
  

The extended gantry appears capable of firing long-range rockets with a range of more than 13,000 kilometers, they said.
  

North Korea is banned under U.N. Security Council resolutions from carrying out any launch using ballistic missile technology.
  

It has defied the resolutions, however, insisting on its right to use the technology for scientific purposes.
  

"We think there is credibility in the intelligence that (North Korean leader) Kim Jong-un has ordered the launch of a satellite to mark the Workers' Party anniversary," said another government source, also requesting anonymity. "We have detected signs of what appears to be the manufacturing of a long-range rocket at an arms factory near Pyongyang."
  

Meanwhile, the North has recently moved its major artillery closer to the western sea border with the South, according to a military official in Seoul.
  

The North has deployed four 122-mm howitzers on the uninhabited Gal Island, just 4.5 kilometers away from the South's Yeonpyeong Island across the Northern Limit Line.  
  

The North used the artillery with the range of 20 kilometers in an attack on Yeonpyeong Island in November 2010. (Yonhap)