A teenager was rushed to hospital for emergency surgery after he and three friends were set upon by a gang of about 15 men in a Perth park.
The 18-year-old suffered “serious facial injuries” in the assault at the city’s South Inch, Police Scotland said.
Another man, also 18, suffered lesser injuries to his face. The pair were with two 18-year-old women at the time.
The “disturbing” assault happened as the group-of-four walked near the park’s pavilion at around 10pm on Saturday night.
A Police Scotland spokesman said: “The large group had been congregating near the tunnels, then verbally abused the victims as they walked past, before following them and attacking them.”
He said: “One of the victims sustained serious facial injuries, which required surgery, and another suffered a minor facial injury.”
Two men in particularly were identified as ringleaders, who were the most responsible for the attack.
The first is described as white, 6th 2in with straight black hair. He was wearing a light blue Stone Island jumper at the time.
The second suspect is also white, about 6ft, bald with what witnesses said was a “noticeably round face.” He was dressed in a hooded top.
The gang of around 15 men were described by police as “young adults”.
Perth City Centre councillor Pete Barrett said: “This is a very disturbing incident and serious assault.
“I hope that the descriptions of these thugs provided by the police leads to their rapid identification and arrest.”
The Liberal Democrat said: “I would encourage anyone who recognises the assailants, or thinks they know who they might be, to get in touch with the police.
“If in doubt please don’t hesitate. It is far better that the police eliminate anyone not involved in this assault than the perpetrators get away with it.”
At the end of November, Police Scotland declared a blitz on large gangs in Perth city centre, amid a worrying rise in antisocial behaviour and violent crime.
It followed the stabbing of a 15-year-old boy in October. Officers said the youngster nearly died after the attack in Moncrieffe Island.
South Inch was one of the areas targeted by police as part of Operation Stung.
SNP city centre councillor Andrew Parrott added: “People should be able to enjoy the South Inch, and anywhere else, without fear or risk of assault.
“I believe that generally Perth remains a safe place, but incidents that demonstrate otherwise must be dealt with appropriately.”
Anyone with information is urged to call police on 101 or freephone Crimestoppers in confidence on 0800 555 111, quoting case number 4415 of March 6.