The U.S. and South Korea have pledged to “advance combat readiness capabilities” near the disputed sea border with North Korea, warning that any aggression by Pyongyang “is not to be tolerated.”

U.S. Defense Secretary Leon Panetta and his South Korean counterpart, Kim Kwan-jin, issued a statement Friday in Seoul.

Panetta told reporters North Korea has demonstrated a “readiness to conduct provocations that costs innocent lives.”

The two defense chiefs also pledged to formulate a bilateral strategy to counter nuclear threats from the isolated regime. They described the North's uranium enrichment program as “a grave threat” which gives Pyongyang a second path to develop nuclear weapons, and increases the possibility that nuclear weapons and technologies will be passed on to “other parties.”

Panetta pledged the U.S. will sustain and enhance its military presence on the Korean Peninsula and in the Asian region despite the threat of deep cutbacks in the U.S. military budget. There are about 28,500 U.S. troops stationed in South Korea.

Tensions have been high on the Korean Peninsula since the deadly sinking of a South Korean warship that Seoul blamed on Pyongyang, followed by North Korea's artillery attack on a South Korean border island that killed four people. The North has denied any responsibility in the sinking of the warship.