SEOUL, South Korea - The most senior U.S. military official delivered a sharp rebuke to China on Wednesday, blaming Asia's top power for failing to rein in its North Korean ally in its escalating dispute with South Korea.

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, blasted China for refusing to condemn North Korea over the Nov. 23 artillery barrage that killed four people on the South Korean island of Yeonpyeong.

He spoke in Seoul, where he met with his South Korean counterpart in a public display of resolve to deter new North Korean aggression. But Mullen directed his most pointed criticism at Beijing.

"The Chinese have enormous influence over the North, influence that no other nation on earth enjoys," said Mullen at a news conference at the South Korean Ministry of National Defense. "And yet, despite a shared interest in reducing tensions, they appear unwilling to use it."

"Even tacit approval of Pyongyang's brazenness leaves all their neighbors asking, 'What will be next?' "

At the joint news conference Wednesday, Han Min Koo, South Korea's top commander, said that rules of engagement were being strengthened to allow commanders on the ground to fire back immediately in case of another North Korean attack.

Geopolitical fault lines dating back to the 1950-53 Korean War have reemerged, with China standing staunchly behind North Korea and the United States and South Korea reaffirming the vows of their long, if occasionally troubled, alliance.

In a show of force designed to deter North Korea and remind China of the United States' military might, the United States and South Korea have been staging war games in the Yellow Sea, much to Beijing's irritation.

The South Korean government is furious that Beijing held both Koreas equally culpable, an echo of its refusal to accept evidence of North Korean guilt in the sinking earlier this year of the Cheonan.

The South Korean military ship was hit by a torpedo that an investigation determined was fired by a North Korean submarine.

"China's overt support for North Korea is blunting the effectiveness of diplomatic measures to curb their behavior," said L. Gordon Flake, a Korea specialist with the Mansfield Foundation.