A man has suffered facial burns after his jacket was set alight as he walked home from a mosque.
West Midlands Police said officers are studying video footage of the attack which has been circulated on social media.
The incident took place in Shenstone Road in Edgbaston, Birmingham, at around 7pm on Monday.
The force said in a statement: “It’s believed the man, who was walking home from Dudley Road Mosque, was approached by a man.
“He spoke to him briefly before spraying him with an unknown substance and then his jacket was set alight, causing burns to his face.
“He was taken to hospital with serious injuries which are thankfully not believed to be life-threatening.”
Officers are aware of a video posted on social media “showing a man being set alight, and we’re examining it as part of our investigations”, the statement added.
Superintendent James Spencer said on Tuesday: “Our officers have been working through the night to establish what happened and who is responsible.
“We’re examining CCTV and speaking to witnesses and are determined to find out who is responsible.
“I’ve been speaking to people this morning, and so I know just how concerned they are and that people are after answers.
“We are determined to find the person responsible and get those answers as soon as possible, and I’d urge the community to work with us and to avoid any speculation at this stage.”
Extra officers will be in the area to speak to the community and to provide reassurance.
Following the attack, Birmingham City Council leader Ian Ward, Cabinet member for social justice, community safety and equalities John Cotton, and ward councillors Sharon Thompson and Marcus Bernasconi said: “This was a horrific attack and our thoughts are with the victim and his family at such a distressing time.
“Councillors and the community safety team are speaking to the family and West Midlands Police. We will continue to offer our support.
“Council officers, local councillors and MP have also been engaging with community groups and local mosques to offer support to the wider community.
“We would urge the community to work with the police and to avoid any speculation at this stage – and also like to thank them for their willingness to share information on this incident.”
Anyone with information has been asked to get in touch with West Midlands Police via Live Chat on the force website or to contact Crimestoppers, anonymously, on 0800 555 111.