The allegation may impact joint statement adopted at the DPRK-U.S. Summit, North Korea warned.
Bad Rabbit is spreading "in a worm-like fashion" between computers.
British-based malware researcher Marcus Hutchins was detained in Las Vegas on Wednesday.
Petya was only masquerading as ransomware. Its real function was to destroy victims' data.
Newly found flaw in widely used networking software is yet to be exploited by hackers.
Cybersecurity firm Symantec said a North Korean hacking group was behind the WannaCry cyberattack.
Security researchers say infected machines are "mining" for a digital currency called Monero.