More than 40 North Korean soldiers were killed or wounded when South Korea returned fire for the North’s artillery attack on Yeonpyeong Island in November 2010, a media report said Friday, quoting a source familiar with the battalion responsible for the assault.

The attack on the South Korean border island killed two marines and two civilians, causing inter-Korean relations to deteriorate to their worst level in decades. The number of North Korean casualties from South Korea’s return fire has not been confirmed.

“I was told by a North Korean battalion commander that more than 10 North Korean soldiers were killed and about 30 others were injured” during the conflict on Nov. 23, 2010, the source told Washington-based Radio Free Asia (RFA).

The RFA said the source was on close terms with officers in the 4th Battalion, the front-line unit responsible for the shelling, and spoke during a recent trip to China.

“The North Korean military is afraid of the South Korean military’s high-tech weaponry, and despite their military leaders’ threats to go to war (with the South), the soldiers have lost a lot of morale,” RFA quoted the source as saying. “Ever since the Yeonpyeong battle, (the North’s) military is reluctant to fight with the South’s military.”

South Korea responded with advanced K9 self-propelled howitzers and dispatched F-16 fighter jets to Yeonpyeong, shortly after the North fired around 170 artillery shells onto the island and its surrounding waters off the west coast.

The communist country accused the South of initiating fire, saying the South had launched artillery shells into its waters earlier that day. South Korean military officials denied that they provoked the North.

North Korea recently said it was ready to fight a “sacred war,” and said large-scale joint military exercises launched by South Korea and the United States this week are tantamount to declaring war against it.

Pyongyang routinely denounces the joint military drills as precursors for an invasion, while Seoul and Washington insist they are defensive in nature.

About 28,500 U.S. troops are stationed in South Korea, a legacy of the 1950-53 Korean War that ended in an armistice, not a peace treaty. (Yonhap News)