North Korea has moved the entrances to the military's howitzer bunkers in the border area to a northward direction from the south, making it more difficult for South Korea and the U.S. to curb the howitzer attacks in a war situation, a government source said Sunday.
  

"Changes have been detected in the shape of the bunkers for self-propelled guns, which belong to artillery units of the North's 4th Corps in Hwanghae Province," the government source said, asking not to be named.
  

"Previously south-oriented doorways of the bunkers have been closed while new ones have been made facing a northward direction," the source noted.
  

He said the change of the doorways' direction makes it difficult for Seoul and Washington to counter North Korea's howitzer attacks in an emergency situation, adding that "the North Korean military seems to have changed it to guard against assault by the allies' combined forces in the time of emergency."
  

Experts said, in a war situation, the allies will now have to fly aircraft over the fortified bunkers to the entries to counter North Korean howitzer attacks, a change that will expose the allies' aircraft to more antiaircraft gun and missile attacks.
  

Previously, the South Korean military had an operational strategy to smash North Korea's howitzers within three minutes upon the launch of the North's attacks before the howitzers withdraw to the bunkers.
  

But the recent change of the bunkers' entries may extend the time needed for the allies to bomb the howitzers, which can reach South Korea's entire capital area.
  

In efforts to strengthen its howitzer attack power in recent years, the North has fortified the bunkers, building up concrete protective walls and 20-centimeter-thick iron doors inside and outside of the bunkers.
  

The government source said in response to the North Korean move, South Korea pushes to renovate its K9 howitzer, extending its range up to 100 kilometers. (Yonhap)