Thousands of taxi drivers upset at Uber's threat to their livelihoods blocked key roads in and near Costa Rica's capital on Tuesday, with dozens arrested amid clashes with police, officials said.

Anti-riot officers intervened to prevent protesters from cutting off access to the country's main airport northwest of San Jose.

In the east of the city, a violent confrontation with police resulted in the arrest of four taxi drivers. TV news images showed a police officer with his face bloodied.

At least 70 other taxi drivers were arrested in other parts of the city for blocking roads, the government said. Police seized some 20 taxis.

The head of Costa Rica's police force, Juan Jose Andrade, said on Twitter that police found nails strewn across one road.

The taxi drivers called the protest to demand the government block Uber's smartphone app.

The US-based internet ride-hailing company operates in Costa Rica without government authorization.

It responded to the taxi protest against it by offering fare discounts to passengers in San Jose.

Uber has grabbed around 35 percent of passengers from taxis in Costa Rica since entering the country mid last year, according to a recent survey by the Cid Gallup company.