Updated

Small groups of masked youths backing a 10-day protest by farmers have clashed with tear gas-firing riot police in Colombia's capital as President Juan Manuel Santos acknowledges what he calls "a crisis" in the agricultural sector.

Thursday's violence followed peaceful marches by about 28,000 university students and others supporting the farmers.

Santos opened talks with the farmers Tuesday and said in a TV address Thursday that their complaints are legitimate and stem from years of neglect. He announced measures to address the complaints, such as removing import tariffs on many types of fertilizers.

The farmers complain of high fertilizer costs and low prices at market such produce as potatoes, onions and milk because of cheaper imports.

They have been blocking highways and battling riot police since last week.