A British football fan has been arrested and detained in the United Arab Emirates after he wore a Qatar national team shirt to a match.

Ali Issa Ahmad, 26, a British Arsenal fan who lives in Wolverhampton, travelled to the UAE for a holiday in January. While he was there he got a ticket for an Asian Cup match between Qatar and Iraq on 22 January. The tournament took place in the UAE between 5 January and 1 February and was won by Qatar.

Ahmad wore a Qatar shirt to the match not knowing that doing so in the UAE is an offence punishable with a large fine and an extended period of imprisonment.

After his initial arrest he was held over claims that he had made false allegations about security officials, a friend of Ahmad told the Guardian.

The UAE embassy said it was investigating the circumstances of the arrest and the Foreign Office (FCO) said it was offering support.

The FCO website in its section containing information for travellers to the UAE warns: “The UAE authorities announced on 7 June 2017 that showing sympathy for Qatar on social media or by any other means of communication is an offence. Offenders could be imprisoned and subject to a substantial fine.”

Its advice adds: “You should respect local traditions, customs, laws and religions at all times. There may be serious penalties for doing something that might not be illegal in the UK.”

The sanctions for “promoting” Qatar are linked to the breaking off of diplomatic relations between the two countries in May 2017. The UAE accused Qatar of undermining security and stability in the region by funding and hosting terror groups.

Ahmad was granted one phone call on 31 January and was able to call his friend Amer Lokie and raise the alarm.

Lokie said: “This is just unspeakable. He just went to watch a football match while he was on holiday in UAE and says he was arrested and beaten after being accused of wearing a football shirt which promoted Qatar. When he managed to call me officials were sitting next to him so he couldn’t say too much. He wasn’t given very long to speak to me and I’m not exactly sure what happened.

“It seems that he was released after being detained, assaulted by the security men in the car and accused of promoting Qatar. He went to the police station to report the assault and was accused of telling lies about the incident.

“We’re not clear about exactly what happened next but he has been held because he is accused of making false allegations against UAE security officials. He said he is being held in a place called Al Sharjar.”

Lokie added: “He loves football so much. He goes to watch lots of football matches in the UK. He’s such a kind and quiet guy. He is the kind of person who always tries to help others.

“He didn’t sound good when he spoke to me on the phone. He was speaking very slowly and he sounded very frightened.”

Lokie said that Ahmad’s phone had been taken by officials and wiped, adding that his friend had told him he was held in a small room for two days.

“He begged us to do whatever we can to get him released so we contacted the Foreign Office and asked them to help get him released,” Lokie said. “He said he would call us back but since then we have not heard anything from him. I am in shock that he was arrested and assaulted because of the football T-shirt he was wearing. We are all so worried about him. This is very serious.”

A UAE embassy spokesperson said: “The United Arab Emirates embassy is looking into allegations that a British citizen has been detained. The UAE is a nation built on the rule of law and respect for individuals. We take any allegation of human rights violations extremely seriously – whether it concerns one of our citizens, or any of the 1.5 million Britons who visit us each year.”

An FCO spokesperson said: “We are providing assistance to a British man arrested in the UAE and are in touch with the local authorities.”

Last November the British academic Matthew Hedges returned to the UK after being accused of spying and jailed for life in UAE. He served seven months of his sentence, mostly in solitary confinement. He was released after receiving a pardon from the UAE authorities.