The Dutch government is investigating whether it failed to heed warnings from Israel about possible attacks on Israeli fans of Maccabi Tel Aviv on Thursday night, Justice Minister David van Wiel acknowledged in a letter to parliament.

“An investigation into possible warning reports from Israel is still ongoing,” Van Wiel said in his letter late Friday night.

At least five people were injured during the attacks on Thursday night and taken to hospital. All were discharged on Friday.

Police said today that four people remained in custody of the 63 brought in.

“The Prosecutor’s Office has stated that it aims to implement speedy justice as much as possible,” Van Wiel said, adding that it was an “absolute priority” to identify every suspect. He also said that the investigation will also examine whether the attacks were organized, with an anti-Semitic motive.

Amsterdam authorities banned demonstrations over the weekend and the government gave police emergency powers in response to the unrest.

Anti-Semitic incidents have increased in the Netherlands following Israel’s attack on Gaza in response to Hamas gunmen’s attacks on Israel in October last year, with many Jewish organizations and schools reporting threats and hateful emails.