Radical students trying to march to the border with North Korea confronted a wall of riot police Monday, turning a symbolic "reunification pilgrimage" into a melee of exploding tear-gas grenades and firebombs.

Hours after President Roh Tae-woo issued a call for direct talks with North Korean leader Kim Il-sung, about 1,000 students attempted to march off the campus of Yonsei University in western Seoul.They were met at the university gate by 7,000 riot police who launched barrages of tear gas and rushed through the biting fog arresting some 500 student leaders, witnesses said.

The students pressed ahead with their banned march in the face of calls from all major political parties - and from opposition leader Kim Dae Jung - to postpone their attempt to meet with North Korean students until after the Summer Olympics next month.

Student leaders had arranged with North Korean student representatives to meet at the border outpost of Panmunjom, 35 miles north of Seoul to talk about reunification of the divided peninsula.

The students believe that holding the Olympics in Seoul without allowing Pyongyang to co-host the games will drive another wedge between the two nations, already split by 40 years of mistrust and militarism spawned by the Korean War.

Earlier Monday, Roh said in a speech marking the 43rd anniversary of Korea's liberation from Japanese rule that he wanted direct talks with his North Korean counterpart, Kim Il-sung.

Roh has said several times in the past that "summit" meetings between the North and South are the best way to solve problems.

Kim Il-sung has been the unchallenged ruler of communist North Korea since 1948.

"On the occasion of this 43rd Liberation Day, I propose to President Kim Il-sung of North Korea to meet with me for talks at the earliest feasible date to work out practical ways to bring about national integration in response to the yearning of our 60 million compatriots," Roh said.

In his speech at Independence Hall, 55 miles southeast of Seoul, Roh said the South Korean people and his government "will not forgive" anyone who tries to disturb the Seoul Summer Olympics, scheduled to begin Sept. 17.

Monday's march began at midday when a group of students walked to the front gate of Yonsei University carrying a banner with the words "Let's Reunify Our Country" written in the blood of some 50 members of the "Reunification Vanguard," witnesses said.