General Leon Laporte said 70 percent of North Korea's ground force of almost one million active duty soldiers were currently deployed south of Pyongyang, capable of attacking its southern neighbour with "little tactical warning."
The size, firepower and proximity of North Korea's conventional forces to Seoul -- coupled with their lethal asymmetric threats -- give North Korea the capability to inflict "great destruction and casualties if they chose to attack," he told a hearing on military construction under the House Appropriations Committee.
Questioned by Florida Representative Allen Boyd whether US-led forces in South Korea were prepared "if a situation in North Korea occurred today," Laporte said: "I am very confident today that we have adequate forces to deter a North Korea attack.
"I am also very confident that our forces on the peninsula are trained and ready," he added in the same breath.
Laporte said that aside from US and South Korean troops, he was confident that American forces in the Pacific, including from Japan, would reinforce the military capability against North Korea if the situation warranted.
The United States has 37,500 soldiers, sailors, airmen and marines and 5,700 civilian defence serving in South Korea.
US and South Korean marines were engaged in live-fire training close to the tense border with North Korea last week as part of drills denounced by Pyongyang as preparations for a preemptive strike.
US authorities say the exercise is purely defensive and designed to improve the ability of allied forces to defend South Korea against external aggression.
The 1950-53 Korean War ended in a fragile armistice and the Korean peninsula remains the world's last Cold War frontier with nearly two million troops ready for combat either side of the tense frontier.
Washington accused the Stalinist state in October 2002 of having a program to enrich uranium and demanded that North Korea completely and verifiably dismantle its nuclear programmes.
Two rounds of six-nation talks on the impasse have made little progress.
Pyongyang has sought security guarantees and economic aid in return for denuclearization while Washington has insisted that a verifiable dismantling of the Stalinist state's nuclear program come first.
Laporte said that North Korea's efforts to strengthen its military remains the most substantial threat to regional peace.
He said that the North Korean ballistic missile inventory included more than 500 Scud missiles that can deliver conventional or chemical weapons across the entire peninsula.
Pyongyang also continues to produce and deploy mediumn range "No Dong" missiles capable of striking cities and military bases in Japan with these same payloads, he said.
"Continued research on a three-stage variant of the "Taepo Dong" missile could provide North Korea the capability to target the continental United States," Laporte said.
He pointed out at the hearing that he saw "no indications" North Korean leader Kim Jong-il's regime would change its "military first" policy, brinkmanship, nuclear challenges, missile proliferation, and illegal activities.
Laporte urged Congress to support the continued deployment of advanced theater missile defense capabilities crucial to protect US forces in the Korean peninsula.
Last year, US fielded short-range Unmanned Aerial Vehicles in the peninsula that improved its tactical capability in intelligence gathering and surveillance, he said.
"The next step is fielding long-range, high-altitude Unmanned Aerial Vehicles that can conduct some of the missions now performed by manned reconnaissance aircraft," he said.