The Welsh first minister has described the sudden and unexplained death of a 24-year-old man from Cardiff hours after his release from custody as “deeply concerning”. South Wales police referred the death of Mohamud Mohammed Hassan after he was arrested following a disturbance in the city to the Independent Office for Police Conduct (IOPC), which has launched an investigation. Police said they were called by the Welsh ambulance service to a “multi-occupancy” property in Roath, shortly after 10.30pm on 9 January. Hassan, who was of Somali heritage, was arrested at his Cardiff home on Friday on suspicion of breach of the peace but released without charge on Saturday morning. Officers said he left custody at around 8.30am. Hours later on Saturday evening he had died with his family saying he had claimed he was assaulted in custody before his death. South Wales police said it had so far found no evidence of excessive force or misconduct. It said its self-referral to the complaints watchdog was standard practice following a death after police contact. The IOPC director for Wales, Catrin Evans, said it would look carefully at the level of force used during the arrest and whether proper assessments were made on Hassan before he was released, but added that preliminary indications were that there was no physical trauma injury to explain the cause of death and toxicology tests would be needed. Speaking in the Welsh parliament, Mark Drakeford, offered his condolences to Hassan’s family. “Our thoughts must be with the family of a young man who was a fit and healthy individual whose death must be properly investigated,” he said. The Welsh first minister said the first step was to allow the IOPC to look into the case. “I expect that to be done vigorously and with full and visible independence,” he said. The Plaid Cymru leader, Adam Price, told the parliament: “Witnesses were reportedly shocked by Mr Hassan’s condition on his release, saying his tracksuit was covered in blood and he had severe injuries and bruising. “There can be no doubt this is a deeply harrowing case and every effort should be made to seek the truth of what happened. Why was Mohamud Hassan arrested, what happened during his arrest, did he have legal representation, was there any after care; why did this young man die?” Price asked the first minister to do “everything in your power to help the family find those answers”. The Plaid leader reminded the parliament of previous controversial investigations involving South Wales police including the murder of Lynette White, which led to the Cardiff Three miscarriage of justice, and the death of schoolboy Christopher Kapessa, following which his mother, Alina Joseph, accused the police of institutional racism. Price asked Drakeford: “Do you understand why so many people of colour sympathise with that statement? The Plaid leader also pointed out that only 2.6% of South Wales police officers were from black and ethnic minority backgrounds when they made up 6.7% of the population. He also said black people in Wales were more likely to end up in prison than their US counterparts. Drakeford replied: “Black lives matter in every aspect of public services and public life here in Wales. That obligation lies with our police services as much as every part of life.” Hassan’s aunt, Zainab Hassan, said she saw her nephew within an hour of his release. “He had lots of wounds on his body and lots of bruises,” she said. “He didn’t have these wounds when he was arrested and when he came out of Cardiff Bay police station, he had them. “Nothing we do is going to bring him back, but we will not rest for a second until we have justice.” On Tuesday afternoon, about 200 people gathered outside Cardiff Bay police station and flares were let off to protest over Hassan’s death. Demonstrators chanted “no justice, no peace” and demanded the force release CCTV of Hassan’s time in custody, while some held signs that read “Black Lives Matter” and “stop police brutality”. One protester, Bianca Ali, 29, said: “We want justice, we want transparency, we want answers, we want the truth.” Hilary Brown, a solicitor and director of Virgo Consultancy, said a complaint had been made to the IOPC, while the family would be seeking an independent pathologist report and called for an independent police force to investigate the issue. Evans said the IOPC “will look carefully at the level of force used during the interaction”, adding: “We will be urgently examining the extensive relevant CCTV footage and body-worn video. Accounts will be gained from the officers involved, and we will be seeking to speak to a number of witnesses to the police attendance on Friday evening and to Mr Hassan’s movements on Saturday after leaving custody. “I would like to reassure people that we will carry out a thorough and independent investigation … An interim report from a postmortem examination is awaited. Preliminary indications are that there is no physical trauma injury to explain a cause of death, and toxicology tests are required.”In a statement South Wales police said: “As part of the South Wales police investigation CCTV and body-worn video has already been, and will continue to be, examined. “This will assist in establishing and understanding the events that took place. Early findings by the force indicate no misconduct issues and no excessive force.” A postmortem examination was due to take place on Tuesday.