Police in Ecuador clashed with ecologists and indigenous people protesting plans to open up a huge Amazon reserve to oil drilling.

Four protesters were detained for a few hours but later released, Interior Minister Jose Serrano said on Tuesday.

President Rafael Correa had announced a plan to declare the Yasuni National Park off limits to drilling in exchange for millions of dollars from other countries, but dumped the scheme earlier this month.

He said he gave up because little money had been offered.

The reserve is said to hold 920 million barrels of oil.

The protesters want a national referendum on whether to drill in the unspoilt area.

Organizers said hundreds of people took part in marches in the capital city Quito and in Cuenca in the south.

Carlos Perez, leader of an indigenous movement called Ecuarunari, said police had fire rubber bullets and there were around 12 people hurt.

Authorities gave no figure, nor would the Red Cross.

The interior minister said newspaper reports that police had used tear gas and rubber bullets were wrong and demanded a rectification.

Correa says he is open to a referendum on drilling in the reserve and challenged protest organizers to come up with the 60,000 signatures needed to prompt one.

The oil believed to be lying under the Yasuni is equivalent to 20 percent of the total reserves of Ecuador, OPEC's smallest member.