Spanish police said Tuesday they had arrested four men suspected of plotting to sabotage the 2023 Vuelta a España by pouring oil on a stretch of highway the cyclists were due to use.

Officers detained the four on Saturday in a wooded area near the town of Suria in the northeastern region of Catalonia, just as they prepared to release 400 liters (88 gallons) of "a liquid similar to motor oil" from two drums onto the road, Spain's National Police said in a statement.

The drums and a hose that stretched from them to the highway "were hidden amongst the vegetation, making it difficult to detect," the statement added.

The third stage of the Vuelta on Monday -- a 158.5-kilometer (98.5-mile) ride from Suria to Arinsal in Andorra -- included that stretch of the highway.

It was won by reigning champion Remco Evenepoel of Belgium.

The four suspects are supporters of Catalan independence, according to far-left Catalan pro-independence group Alerta Solidaria, which fiercely opposes the passage of the Vuelta through the region, calling it "colonialist."

They have been charged with membership in a criminal group, public disorder and environmental offences.

The four appeared before a court on Monday in Solsana, which released them but banned them from going withing 500 meters of roads along which the cycle race was to pass as it goes through Catalonia, their lawyer Eva Pous told Catalan media.

Along with the Tour de France and the Giro d'Italia, the Vuelta is one of cycling's prestigious Grand Tours.

This is the 78th edition of the race and ends in Madrid on Sept. 17 after 21 stages and 3,153.8 kilometers.