In June, three non-governmental organisations filed a lawsuit accusing the bank of financing the purchase of "80 tonnes of arms used to carry out genocide" by the Hutu regime, even though "the bank had to have known the genocidal intentions of the country's authorities".
The Paris judiciary confirmed on Monday that it opened an investigation for "complicity in genocide and complicity in crimes against humanity" on 22 August, and asked the Paris genocide and war crimes division, which is already handling 25 other cases linked to the Rwandan genocide, to run the probe.
The lawsuit was filed in France by Sherpa, which defends victims of economic crimes; Ibuka France, a Rwanda victims' association; and the France-based Collective of Civil Parties for Rwanda, which pursues claims against genocide suspects.
The NGOs say BNP authorised the transfer of 1.1 million euros at current rates to the regime in June 1994, one month after the United Nations had placed an embargo on weapons deliveries to Rwanda.
BNP is France's biggest bank and among the world's top 10.
The plaintiffs allege that BNP authorised the transfer of the money that was held by Rwanda's national bank (BNR) to an account held at Swiss bank UBP by Willem Tertius Ehlers, a South African intermediary who owned an arms-dealing brokerage called Delta Aero.
The four-month genocide led to the massacre of about 800,000 people, mostly from Rwanda's Tutsi minority.
Kigali has repeatedly accused Paris of having a hand in the genocide and of being slow to prosecute some of its kingpins living in France.
The case is the first time a French bank is under suspicion of being involved in the genocide.