South Korean police said Sunday that they were questioning dozens of protesters after violence broke out at a rally denouncing the government's handling of a ferry disaster that killed more than 300 people a year ago.

Police used water cannons and pepper spray to break up thousands of protesters in the capital, Seoul, on Saturday night. Dozens of police officers and protesters were injured during the demonstration.

The protesters, led by relatives of victims of the ferry disaster, tried unsuccessfully to march to the presidential Blue House. More than 70 police buses used to block a downtown street leading to the Blue House were damaged or vandalized, said an official from the National Police Agency, who spoke on condition of anonymity, citing office rules.

The official said around 80 people were being questioned over the demonstration. Twenty others who were also detained have been released.

The demonstration capped off a week of vigils and rallies commemorating the anniversary of the ferry disaster. A total of 304 people -- most of them students from a single high school -- died when the ferry Sewol sank off South Korea's southwest coast on April 16, 2014.

There's frustration among South Koreans who see their government as having failed to make meaningful improvements to safety standards and hold high-level officials accountable for a disaster blamed in part on incompetence and corruption.

The relatives of the victims and their supporters have been calling for the government to accept a more thorough investigation into the cause of the sinking and provide a more detailed plan to salvage the ship.

Prosecutors have blamed negligence by crew members, excessive cargo and improper storage for the sinking, along with slow rescue efforts. Relatives of the victims say the prosecution's investigation was insufficient and have called for the establishment of an independent committee to look more deeply into the government's responsibility for the sinking and the high death toll.