"In the near term, the Republic of Korea must develop a systematic missile defense solution to protect its critical civilian and military command capabilities, critical infrastructure and population centers," said Lieutenant General Walter Sharp in a written testimony to a US Senate military panel.

"South Korean military and civilian facilities are currently highly vulnerable to North Korean missile attacks," he warned in the report, released on the panel's website Friday.

His testimony came as North Korea announced Thursday it was suspending all dialogue with South Korea and closing the border to Seoul officials, its toughest action in a week of growing cross-border tensions.

Sharp, who is tipped to succeed General Burwell Bell also as chief of the combined US-South Korea command, said PAC-3 Patriot missile system upgrades and improved munitions had significantly enhanced US ability to protect critical American facilities in South Korea.

"However, there is a significant shortage of PAC-3 missiles currently available on the peninsula to counter the North Korean missile threat," he noted.

In addition, South Korea, which recently announced plans to purchase eight PAC-2 Patriot firing units, does not currently possess capability that can fully integrate with the US ballistic missile defense systems, he said.

But Seoul has plans to begin integrating with US ballistic missile defense systems, he said, without giving any time frame.

Sharp, who has served in South Korea previously, said he was "very familiar" with the threat posed to that country.

He warned however that "North Korea still has the capacity to inflict major destruction and significant military and civilian casualties in South Korea, with little or no warning."

Sharp also said that the US intelligence community "remains uncertain" about North Korean leader Kim Jong-Il's commitment to full denuclearization as promised under a six-nation deal to end the hardline communist state's atomic weapons drive.

The deal is stalled by delays in the North's promised declaration of all its nuclear activities.

Fresh North-South tensions arose after new South Korean President Lee Myung-Bak, a conservative who took office on February 25, adopted a tougher line on relations.

His liberal predecessors had practised a decade-long "sunshine" engagement policy, under which aid and investment worth billions of dollars flowed northwards and cross-border exchanges expanded hugely.

But Lee wants to link economic aid to the North's progress in nuclear disarmament and raise its widely criticised human rights policy.