Five radical students armed with bombs and knives seized a U.S. Information Service office today and detonated two bombs and started a fire before police overpowered them. Two of the students brandishing explosive devices and draped in South Korean flags stood at shattered windows on the second floor yelling ``Yankee go home'' as riot police ringed the building. U.S. Embassy officials said they had no reports of injuries, but the attackers smashed windows and set a fire in a periodical storage room. Thick smoke filled part of the building located in the heart of Seoul. People inside the building at the time of the attack, including at least one American, were not detained by the radicals. The students, who said they were members of the ``Young Student Suicide Group'' claimed they had 18 bombs and screamed at surrounding police to stay away. They tossed down a statement charging the United States was attempting to make South Korea a colony. ``Yankees stay out of Korea,'' the students yelled. A police officer said it was unclear how many of the explosive devices the attackers had. The bombs were crude chemical devices, possibly some kind of plastic explosive, he said. About 200 radical students hurling firebombs and rocks clashed with riot police about an hour later outside Myungdong Cathedral. Police fired volleys of tear gas at the students who yelled slogans denouncing President-elect Roh Tae-woo, who is to be sworn in Thursday. Hundreds of protesters had gathered at the cathedral less than a mile from the U.S. Information Service office earlier in the afternoon for an anti-government protest. ``Down with Roh Tae-woo,'' the students yelled. Some of the attackers were reading in the office's library when there was a large explosion in a nearby roon and they suddenly pulled out bombs and started screaming slogans, eyewitnesses said. At least one of the attackers pulled out a knife and brandished it, they said. ``He was kind of crazy-eyed,'' said Paul Wadden, a visiting American teacher who was reading in the library at the time. The attackers smashed three windows overlooking the main street outside and two of them stood shouting slogans out into the street and brandishing bombs and cigaretee lighters. Riot police stood on the sidewalk below with shields covering their heads and shattered glass covered the street. The students tossed at least one bomb into the street where it exploded harmlessly, eyewitnesses said. A second bomb was tossed out, but did not explode, they said. People caught in the library said the students did not attempt to detain them and they were able to leave after recovering from their initial shock. Wadden said he and other people were prevented from leaving downstairs for up to 10 minutes by building guards. There were about 40 people in the library at the time, most of them Koreans, eyewitnesses said. Police who entered the building by the rear entrance overpowered the protesters about 30 minutes after the attack began. The students were taken out of the building in a bus with covered windows. U.S. Embassy officials said South Korean riot police entered the building at their request. Japanese Prime Minister Noboru Takeshita arrived at the Lotte Hotel across the street from the U.S. Information Service office just as the incident ended, officials said. Takeshita is in Seoul for Roh's inauguration. American diplomats, who spoke on condition of anonymity, said they did not know why the students attacked the U.S. facility. ``We have no idea what the motivation was,'' an embassy official said. The United States is South Korea's chief ally. Washington has 40,000 troops in South Korea under a mutual defense pact against communist North Korea. The U.S. Information Service provides reading material and other materials on the United States and operates libraries and information centers around the world in conjunction with American embassies. The service office in Seoul is located about half a mile from the American Embassy. The same office was seized by 73 radical students for four days in May, 1985 as an anti-American protest. They ended the occupation peacefully and some later received prison sentences. U.S. Embassy officials were unable to explain today how the attackers were able to bring weapons into the well-guarded building. Visitors must pass a metal detector, present identification and have their bags searched and there are police guards inside and outside. The statement by the students denounced Roh as a puppet who had been installed by the United States. South Korean radicals have repeatedly charged the United States has kept a series of authoritarian governments in power in South Korea. Roh, a former general, won the first democratic elections in 16 years last December.