The diplomatic escalation follows the Jan. 1 fire at Le Constellation nightclub in the Swiss resort of Crans-Montana, which broke out during New Year celebrations shortly after 1 a.m., killing 40 people and injuring 116.
Investigators believe indoor pyrotechnic sparklers attached to champagne bottles ignited flammable acoustic foam on the ceiling, triggering a rapid flashover that engulfed the packed basement venue within seconds.
Swiss prosecutors opened a criminal investigation into the bar’s owners on suspicion of negligent homicide, bodily harm and arson.
Jacques Moretti, one of the bar’s co-owners, had been detained earlier this month as a flight risk before a Swiss court ordered his release on bail on Friday.