Spanish riot police have clashed with protesters outside Barcelona's airport Monday after the Supreme Court sentenced nine former Catalan separatist leaders to lengthy prison terms for their attempt to declare independence from Spain in 2017.

Witnesses say police with batons charged at the protesters who were blocking the entrance to El Prat airport.

Spain Hands Catalans Lengthy Prison Terms Over Secession Bid The landmark ruling, after a four-month trial, inflamed independence supporters in the northeastern region bordering France where Catalan identity is a passionate issue

Spain's airport operator says that at least 20 flights were canceled.

Protesters in the Catalan region also stopped some train service in the region by placing wood on the tracks and blocking roads.

The protesters converged on the transportation hubs Monday after Spain's high court sentenced Catalan separatist leaders to between nine and 13 years in prison for their role in pushing for the region's independence.

The former regional vice president, Oriol Junqueras, received the longest prison term of 13 years behind bars for sedition and misuse of public funds.

The court found three other defendants guilty only of disobedience and did not sentence them to prison.

The court, however, acquitted all defendants of the most severe charge, rebellion.

The former head of Catalonia's regional government called the Monday ruling an "atrocity."

Carles Puigdemont wrote on Twitter: "100 years in prison in total. An atrocity. Now more than ever ... It is time to react like never before. For the future of our sons and daughters. For democracy. For Europe. For Catalonia."

Puigdemont was not a defendant in the landmark ruling over the banned referendum and short-lived independence declaration because he fled to Belgium, where he now lives in self-imposed exile.

After its ruling, the Supreme Court issued a European arrest warrant for Puigdemont.

Catalan's current regional leader, Quim Torra, called the court's ruling an insult to democracy.

Spain's caretaker prime minister, Pedro Sanchez, said in a statement broadcast on live television that the sentences of the Catalan separatists must be carried out.

He also said he hoped that the sentences will help to "turn the page" in relations between Catalonia and greater Spain.