Speaking to the La Stampa news outlet, cabinet secretary Giancarlo Giorgetti said that the League's loyalty to coalition partner M5S was unreasonable and couldn't last forever.
"Faced with the 5Stars movement's reiterated attacks, (Italian Deputy Prime Minister and League leader Matteo) Salvini shows a loyalty (to his coalition partner) that is unreasonable… things cannot last forever", Giorgetti said.
The senior official also said that Prime Minister Giuseppe Conte wasn't neutral as his name was put forward by the M5S movement.
Following the launch of the investigation, M5S called for Siri to step down, but League Leader Matteo Salvini fired back saying that his party had never demanded that M5S politicians resign over investigations.
Commenting on the situation, 5-Star Movement's chief Luigi Di Maio wrote on Facebook that the League was threatening to bring down the government over the investigation.