Microsoft hit back at Google on Monday over the search company’s attempt to derail its bid for Yahoo, threatening to fight back through the regulators if its ambitions were stymied by any partnership between the two.

The flare-up came as Yahoo’s options for finding a “white knight” to save the internet company from Microsoft’s cash-and-stock offer, valued on Monday at $43bn (£22bn), appeared to be narrowing fast. News Corp, which last year proposed merging its MySpace business with Yahoo, and NBC Universal both ruled themselves out. “We are definitely not going to make a bid for Yahoo,” said Rupert Murdoch, News Corp chairman.