Exchange and clearing house operator Intercontinental Exchange said it was considering making an offer for the London Stock Exchange Group.
The move could derail Deutsche Boerse's potential tie-up with the British company.
In a statement, ICE said it had not yet approached the board of LSEG and no decision has been made as to whether to pursue such an offer.
LSEG, which had a market value of $13 billion as of yesterday's close, said it had not received a proposal from ICE and that its talks with Deutsche Boerse were continuing.
Bloomberg, which first reported ICE's interest, also said CME Group is working with advisers to potentially challenge a deal between LSEG and Deutsche Boerse, citing people familiar with the matter.
LSEG and Deutsche Boerse last week confirmed they were in talks to create a European trading powerhouse and propel the companies to a similar scale as US exchange ICE.
ICE has taken a huge slice of the European derivatives market.
Atlanta-based ICE must make an offer for LSEG no later than March 29.
Under British takeover rules, Deutsche Boerse must either make an offer or announce it will not do so by March 22, unless it obtains an extension from the UK mergers regulator.
