Japanese conglomerate SoftBank Group's Vision Fund had invested in a $2.5 billion private equity fund set up by former US Treasury secretary Steven Mnuchin, the Financial Times reported on Wednesday.

SoftBank's investment in Mnuchin's Liberty Strategic Capital came alongside sovereign wealth funds in the Middle East including Saudi Arabia's Public Investment Fund (PIF) and Abu Dhabi's Mubadala, the report said.

In a statement to the FT, SoftBank confirmed it had invested in Mnuchin's private equity firm, but it was unclear how much the Japanese company had contributed to the fund.

Mubadala spokesperson told Reuters it will participate in the fund with a contribution of roughly 2% of the total amount raised so far.

Liberty Strategic Capital, which was launched earlier this year, is a private equity capital firm based in Israel, according to startup data platform PitchBook SoftBank and PIF did not immediately respond to Reuters' request for a comment, while Reuters could not immediately reach out to Liberty Strategic Capital.

Bloomberg News, which first reported about the Mnuchin fundraising this week, said most of the backing came from Middle Eastern investors including the PIF.