BELGRADE, Serbia - Serb rioters broke into the U.S. Embassy Thursday and set fire to an office after a massive protest against Kosovo's independence that drew an estimated 150,000 people. Masked attackers broke into the building, which has been closed this week, and tried to throw furniture from an office. A blaze broke out inside one of the offices and parts of the facade also caught fire. Authorities drove armored jeeps down the street and fired tear gas to clear the crowd. The protesters dispersed into side streets where they continued clashing with authorities. The neighboring Croatian Embassy also was...