US exchanges Nasdaq and ICE have mounted a 11.3 billion US dollars bid for NYSE Euronext, topping a previous offer from Deutsche Boerse. The bid compares with Deutsche Boerse's offer of 10.2bn.
But the move could raise competition questions, as it would bring together the two largest US stock exchanges.
The Deutsche Boerse bid itself is also likely to raise regulation issues, as a deal would create a massive presence in certain European financial products.
The Deutsche plan has also attracted political opposition from those against the idea of a foreign company taking over a Wall Street brand.
The new offer, valued at 42.50 USD per share, is 27% above the company's valuation before Deutsche Boerse's initial bid in February.
ICE, an Atlanta-based futures specialist, is interested in NYSE's derivatives business while Nasdaq would like the stock exchanges and options businesses.
NYSE's stock surged 12.6%, ICE lost 3.1% while Nasdaq OMX rose 9.3%.
NYSE Euronext said its board would carefully review the new offer and recommended that shareholders should take no action pending its review.