SEOUL, South Korea -- South Korea put its military on heightened alert for any North Korean attempt to raise tension on the Korean Peninsula while the world is distracted by the outbreak of war in Iraq.
"We expect North Korea to be cautious, but we have strengthened our alert status and our early warning status in response to possible North Korean attempts to increase tensions," presidential spokeswoman Song Kyoung Hee said.
The North said it also was boosting its military readiness, saying it feared a U.S. attack.
"We will strengthen our readiness in every possible way to meet whatever military options the U.S. imperialists will take against us," said Rodong Sinmun, the North's most prominent state newspaper.
In South Korea, about 4,000 demonstrators gathered near the U.S. Embassy in Seoul to protest the war in Iraq. They demanded South Korea withdraw its support.
Hundreds of protesters, including many college students, kicked and punched riot police who blocked them from approaching the embassy. Police fought back with shields and batons. No arrests or injuries were reported.
Tensions on the Korean Peninsula have been high since October, when U.S. officials said the North admitted having a program to enrich uranium.
With the United States focused on Iraq, experts fear North Korea might use the opportunity to test a long-range missile or reprocess spent nuclear fuel to make atomic bombs. That would be viewed as an attempt to force Washington into direct negotiations over its nuclear programs.
In a televised address, South Korean President Roh Moo Hyun vowed to ensure that the Iraqi war does not worsen the situation on the Korean Peninsula.
"I believe the war on Iraq was an inevitable measure to eliminate weapons of mass destruction as quickly as possible, at a time when diplomatic efforts to resolve the issue peacefully have failed," he said.
After presiding over a National Security Council meeting, Roh said his military has strengthened its vigilance and national police have beefed up security to guard against possible terrorist attacks.
Roh's security adviser, Ra Jong Il, said there were no reports of unusual movements by the North Korean military.
The South Korean Unification Ministry urged North Korea "not to take additional measures that will undermine the stability of the Korean Peninsula and the international community."
Earlier Thursday, Vice President Dick Cheney called Roh to explain Washington's decision to attack Iraq, said Song, Roh's spokeswoman.
Roh said South Korea would dispatch noncombat troops, including military engineers and medics, to help with the Iraq war. He also pledged to protect U.S. citizens and facilities in South Korea from possible terrorist attacks, the spokeswoman said.
Police patrols will be boosted at nearly 700 foreign facilities across South Korea, including embassies and diplomats' residences, which could be targeted for attack by terrorists or violent protesters.
WAR GAMES: Hundreds of U.S. Marines stormed a South Korean beach today, carrying out war games that North Korea charges are a prelude to an invasion.
The maneuvers, supported by fighter jets from warships just off shore, came as other U.S. troops crossed into Iraq in a march to disarm Saddam Hussein.
Both South Korean and U.S. Marines came ashore on amphibious assault vehicles amid mock explosions. Waves of helicopters and fighter jets droned overhead during the exercises, part of annual maneuvers.