BOGOTA - (AP) -- Police foiled an apparent plot to assassinate President Alvaro Uribe after a search uncovered gas cylinders loaded with explosives near the runway of an airport in the northern city of Valledupar ahead of a presidential visit, authorities announced Saturday.

The cylinders were discovered Friday morning as police combed the grounds of the airport a day before the president's visit. Authorities said it appeared they were planted about 20 days ago.

Despite the threat, Uribe went to Valledupar as planned and held a community meeting Saturday.

''I want to ask all the citizens of Valledupar to help us with any information about who planted these cylinders,'' Uribe said.

The nation's largest guerrilla group, the Revolutionary Armed Forces of Colombia, or FARC, has tried several times to assassinate Uribe, who has launched an aggressive military crackdown on the leftist insurgents.

The cylinders found in Valledupar match weapons generally used by the FARC, but it was not clear who was responsible for planning the attack, said Uribe's spokesman, Ricardo Galan.

The last attempt on Uribe's life came about six months ago, Galan said. Unidentified assailants buried cylinders and mortars at an airport in Cali that were discovered a day before Uribe traveled there.