HONG KONG (AP) — Hong Kong police have detained six men, some with links to triads, following a violent attack on pro-democracy protesters at a subway station that saw dozens injured.

Senior police official Chan Tin-chu said the men, aged between 24 and 54, were held being Monday for "unlawful assembly" and will be investigated for taking part in the attack late Sunday night. He said police are still investigating the motive for the attack and further arrests are expected.

A gang of white-clad men beat up anti-government protesters and others inside a subway station with metal rods and wooden poles, injuring 45 people including one in critical condition. The police have been criticized for a slow response, and Hong Kong leader Carrie Lam denied the government colluded with the assailants.