Updated

North Korea warned South Korea on Sunday of "unexpected consequences" if Seoul displays Christmas lights near the tense border, and vowed to retaliate for what it called "psychological warfare."

The South's defense ministry said earlier it was considering a request by a Seoul church group to put up Christmas lights on a steel tower shaped like a tree atop a military-controlled hill near the border.

The North's official website, Uriminzokkiri, called the plan "a mean attempt for psychological warfare" against the communist state and threatened to retaliate immediately if the lights are switched on.

The 511-feet hill in the South, about two miles from the border, is within range of North Korean gunfire.

The tree-shaped, 98-feet high steel structure is illuminated by thousands of small light bulbs and can be seen from the North's major city of Kaesong just north of the border, according to media reports.

"The enemy warmongers ... should be aware that they should be held responsible entirely for any unexpected consequences that may be caused by their scheme," Uriminzokkiri said. "This issue ... is not something to be ignored quietly."

The two Koreas in 2004 reached a deal to halt official-level cross-border propaganda and the South stopped its annual Christmas illumination ceremony.

But Seoul resumed the ceremony last December amid high military tensions with Pyongyang.

Cross-border ties have been icy since the South accused the North of torpedoing its warship with the loss of 46 lives in March 2010.

Pyongyang denied involvement, but went on to shell a border island in November 2010 that left four South Koreans dead and sparked fears of war.

The North has previously accused the South of displaying Christmas lights to spread Christianity among its people and soldiers.