Some 2,000 activists and students rallied near the main U.S. military base in Seoul on Saturday, demanding an end to South Korea-U.S. alliance. Several blocks away, 500 demonstrators marched in support of the Americans.

The protests highlighted the division among South Koreans on how they view their nation's closest ally and biggest trade partner amid tensions over North Korea's suspected development of nuclear weapons.

"Throw out South Korea-U.S. alliance! Let's preserve peace through South-North cooperation!" read banners held by the anti-U.S. group near Yongsan Garrison in central Seoul.

Occupying a six-lane boulevard in front of the American base, about 2,000 protesters demanded the withdrawal of U.S. troops stationed in South Korea.

"As long as the U.S. military stays here, there will be no peace on the Korean peninsula," said Kwon Young-kil, a protest leader and head of the Democratic Labor Party (search).

The so-called "pro-unification" activists have been critical of the U.S. policy toward North Korea in efforts to resolve the nuclear tension.

They supported North Korea's demand for a nonaggression treaty with the United States in return for giving up its nuclear programs. Washington rejects such a treaty, but says it could provide a less formal guarantee.

About 550 yards away, 500 Korean War veterans and activists gathered in a pro-U.S. rally, many waving both South Korean and U.S. flags. They criticized anti-U.S. protesters of hurting the "blood-tied alliance" between the South Korea and the United States, which fought with South Korea against communist North Korea in the 1950-53 Korean War.

Although most South Koreans support the U.S. military presence, the deaths of two Korean girls run over by an U.S. military vehicle last year had triggered large anti-U.S. protests throughout South Korea late last year.

The United States keeps 37,000 troops in South Korea, a legacy of the Korean War that ended in a cease-fire but left the peninsula divided.