MADRID — Catalan activists on Monday marked the first anniversary of their disputed independence referendum by blocking train tracks and roads across Spain’s restive northeastern region and trying to break into the Catalan Parliament, underlining how charged the conflict over separatism remains.

Early on Monday, separatist activists briefly blocked the tracks of the high-speed train that links Barcelona, the capital of Catalonia, to the city of Girona to the north. They also cut off some highways, as well as the most important roads that cross Barcelona. In Girona, they broke into a government building to replace the Spanish flag with the separatist Catalan flag.

By late afternoon, tens of thousands of demonstrators had taken to the streets of downtown Barcelona. Some radical militants also surrounded Police Headquarters and Parliament.

The police responded by making several charges against the militants. Toward midnight, the police managed to disperse the last protesters, amid some minor clashes.