SEOUL, South Korea – One month after a deadly exchange of artillery fire, the two Koreas ramped up their rhetoric Thursday, with South Korea’s president pledging unsparing retaliation if attacked again and a top North Korean official threatening a “sacred” nuclear war if provoked.

South Korean troops, tanks and fighter jets put on a thundering display of force as President Lee Myung-bak visited with soldiers at a base near the border, while North Korea’s elite marked a key military anniversary by lashing out at the South for encouraging war.

For both countries, the rallying cries and military maneuvers mainly seemed designed to build support at home. But they raised fears anew of all-out war on a peninsula that New Mexico Gov. Bill Richardson called a “tinderbox” after returning from a visit to the North Korean capital this week.

The two Koreas and their allies called a truce in 1953 to end three years of devastating war, but violence has flared up from time to time, most recently in the disputed waters off their west coast. North Korea does not recognize the maritime line drawn by U.N. forces, and the territorial dispute in the Yellow Sea has erupted into deadly naval skirmishes.

In March, a South Korean warship went down in the western waters, killing 46 sailors. And a month ago, South Korean live-fire drills in nearby waters triggered a North Korean artillery shower on Yeonpyeong Island that killed four South Koreans.

Caught by surprise, Seoul since has beefed up its rules of engagement and has staged military drills, including joint exercises with U.S. troops, meant to remind the North of its superior firepower. The South even carried out provocative artillery drills from Yeonpyeong Island on Monday in a bold dare to the North to retaliate.

On Wednesday, rifle-toting marines ringed a hillside near the border where a Christian group lit a steel tower dressed up as a twinkling Christmas tree — a structure easily visible from atheist North Korea. Notes left on participants’ chairs advised them to take cover and seek shelter if attacked.

The drills continued Thursday, with tanks firing artillery and fighter jets dropping bombs at training grounds in Pocheon, some 20 miles from the North.

After days of showing restraint, North Korea condemned the drills as a “grave military provocation.”