ABOARD THE USS CURTIS WILBUR -- U.S. and South Korean naval ships fired artillery and dropped anti-submarine bombs off South Korea's east coast Tuesday, the third day of high-profile military maneuvers intended to warn North Korea against any aggression.

The dramatic show of force comes four months after a South Korean warship sank in the waters off the Koreas' west coast, killing 46 sailors. An international team of investigators determined that a North Korean submarine fired a torpedo that sank the ship in what Seoul called the worst military attack on it since the 1950-53 Korean War.

The Korean peninsula technically remains in a state of war because the conflict ended in a truce, not a peace treaty. On Tuesday, both Koreas and the U.S. marked the 57th anniversary of the signing of the armistice against the backdrop of the military drills.

"Since our nation's founding, the United States has relied on our armed forces to ensure our safety and security at home, and to protect lives and liberties around the globe," President Barack Obama said in a statement marking the anniversary. "I call upon all Americans to observe this day with appropriate ceremonies and activities that honor our distinguished Korean War veterans."

In Pyongyang, soldiers and citizens marked the anniversary by laying bouquets at the foot of the Korean War memorial in the capital city, footage from TV news agency APTN showed.

North Korea, which denies any role in the sinking of the Cheonan, has strongly protested the exercises as a provocation. In flourishes of rhetoric typical of the regime, the regime has vowed a "nuclear" response in recent days.

"This is an impure attempt to stifle (North Korea) by means of armed force," North Korean army officer Hong Sung Chol told APTN in Pyongyang. "If the U.S. imperialists ignite war again, our army and people will totally uproot the source of the war under the leadership of our brilliant commander, Gen. Kim Jong Il."

The regime has also pressed its demand for a peace treaty.

"Military tension and the danger of war on the Korean peninsula would not be addressed for good unless the U.S. abandons its hostile policy (against the North) and replaces the armistice with a peace treaty," the government-run Minju Joson newspaper said in commentary carried by the official Korean Central News Agency.

North Korea wants to establish diplomatic relations with Washington to guarantee that the U.S., which has 28,500 troops in South Korea, won't invade and topple Kim Jong Il's government. Pyongyang cites the presence of U.S. troops on South Korean soil as a key reason for building up its atomic program.

The U.S. repeatedly has said it has no intention of attacking the North, but sought to show with the military drills that its solidarity with South Korea remains as strong as ever.

So far, there was no sign North Korea was preparing to mount the defense it warned of in the days before the drills began Sunday, military officials said.

The exercises, dubbed "Invincible Spirit," involve about 20 ships, 200 aircraft and about 8,000 U.S. and South Korean sailors. Most of the firepower has been flying off the decks of the USS George Washington, a U.S. supercarrier that can carry up to 70 aircraft and more than 5,000 sailors and aviators.

"It's been a success," Cmdr. Paul Hogue, commanding officer of the U.S. destroyer Curtis Wilbur. "It's a show of force, a deterrent."

South Korean Defense Minister Kim Tae-young and lawmakers boarded the aircraft carrier Tuesday to boost troop morale.

The Cheonan disaster was devastating but has galvanized the South Korean navy, Capt. Kim Seong-joon said aboard the Curtis Wilbur.

"Our navy was sad at first, then angry. I think we need this exercise," he said.