The report by a task force set up by the government to investigate allegations of doping in Kenyan sport says there are "strong suggestions" that Treu of South Africa and his assistants have violated anti-doping rules after introducing the supplements to players.
There was "a concoction they (the coaches) gave players to drink at the beginning and end of training," Moni Wekesa, the chairperson of the task force that investigated, told The Associated Press on Monday.
The report says the Kenyan players would stop taking the supplement a few days before competing.
Wekesa said that tests performed on the supplements in January were positive for steroids, and the Kenya Rugby Union (KRU) was immediately informed.
The KRU then handed over all the supplements and stopped giving them to players, Wekesa said.
The report said that Treu, who coached South Africa to the IRB Sevens Series title in 2009 and joined Kenya's team as head coach last year, introduced new supplements to the team after arriving.
"Samples of these were retrieved from the union and subjected to laboratory analysis and were found to contain steroids," the report, which has been made public, said.
Kenya is one of the core teams in the IRB Sevens World Series.
The report said Treu, strength and conditioning coach Graham Bentz, assistant coach Felix Ochieng, attack coach Vuyo Zangqa (a former Blitzbok) and conditioning coaches George Kimani and Michael Owino should be "subjected to a disciplinary process" by regional anti-doping authorities.
It also suggested the nation's 15-a-side rugby head coach and assistant coach face anti-doping disciplinary procedures.
The report has been sent to Kenya's government, which commissioned the investigation, and the World Anti-Doping Agency's regional office in Cape Town, South Africa, Wekesa said.
The Kenya Rugby Union and WADA's office in South Africa didn't immediately respond to telephone calls from the AP seeking comment.
The investigation by the task team initially focused on Kenya's No 1 sport, athletics, after German broadcaster ARD alleged widespread doping in the East African nation's world-beating runners in a documentary aired in 2012.
Kenya came under pressure from WADA to investigate after a spike in positive doping tests by its athletes in recent years.
Wekesa's report also found problems in anti-doping measures in Kenyan athletics, football and other sports.
"It came out that a lot of prohibited substances, some recreational, others sophisticated, are commonly abused across all sports," the report said.