Greek riot police clashed with residents of a town outside Athens who were protesting plans to build a landfill to store the capital's garbage. More than 20 were injured Thursday, officials said.

Three riot policemen and at least 20 suspected protesters were hospitalized after the clashes on the edge of the town of Keratea, police and public health officials said.

Protesters pelted riot police with rocks and firebombs. Officers responded with tear gas, which wafted through the town, sending residents scurrying for cover as a police helicopter flew overhead.

Earlier, another group of demonstrators cut a shoulder-high trench across a highway outside Keratea, which has been the scene of frequent riots and road blockades since December.

The planned garbage dump has prompted several months of violent protests from residents. Protest organizers argue the proposed landfill is too close to a residential area and would also damage an ancient site, which they say has not been properly excavated.

Government spokesman Giorgos Petalotis condemned the protesters and said the government had no intention of abandoning its plans to build the landfill, which it said would ease problems at Athens' single garbage dump.

"We are the only authority that has a comprehensive plans for (greater Athens') regional development ... we will not abandon the effort that has been made and is currently being made to build this new facility," he said.

A section of the busy road near Keratea -- linking Athens to the port of Lavrio 30 miles to the south -- has been closed for most of the year.

Protesters used excavators to dig the trenches across the road at two different points and pile up the rubble beside them on the pavement. Clashes first broke out when Environment Ministry trucks, escorted by riot police, arrived to move the rubble.

Keratea residents first set up road blocks in December, demanding authorities scrap the plans for the dump.

The town's municipal officials, who support and have helped organize the protests, say they have asked to meet officials from Greece's central government to find a solution, but have not been granted an opportunity to have their demands heard.