BOGOTA, Colombia (CNN) -- Several hundred masked demonstrators fought running battles Thursday with riot police on the campus of this capital city's largest public university to protest the planned visit of U.S. President Bush.

The demonstrators threw rocks and homemade explosives and launched fireworks through PVC tubes.

Police responded by firing water cannon and tear gas at the demonstrators, who kept up their efforts for three and a half hours.

Student leaders of the protest said they oppose Bush's visit because they oppose what they see as U.S. meddling in Colombia's internal affairs and oppose U.S. funding for the anti-drug and counter-insurgency efforts in Colombia.

They also oppose Washington's efforts to push through free-trade deals.

Bush is on a seven-day trip to Latin America. He is slated to spend a few hours in Bogota on Sunday, when he is to meet with President Alvaro Uribe.

Bush faces opposition in Congress over sending more U.S. money to Uribe's government, which is involved in a domestic scandal over alleged links to right-wing militia death squads.

-- CNN's Karl Penhaul