It looks like Bud brewer AB InBev is gearing up to go hostile in its bid to buy rival SABMiller.

The board of SABMiller spurned a cash proposal worth $104 billion on Wednesday, saying it wasn't high enough.

So Anheuser-Busch InBev on Thursday appealed directly to SABMiller (SBMRY) shareholders to back the bid, signaling it might be prepared to launch a formal takeover offer without a blessing from the board.

AB InBev (BUD) said its proposal to buy the company was a great deal for SABMiller investors.

"The board of SABMiller has refused to meaningfully engage with us," said AB InBev CEO Carlos Brito. "If shareholders agree that we should be in proper discussions, they should voice their views and should not allow the board of SABMiller to frustrate this process and let this opportunity slip away."

SABMiller's biggest shareholder -- the Altria Group (MO) -- has already said it would be prepared to accept the offer, which is worth £42.15 ($47.60) per share, but the second biggest shareholder voted with SABMiller management and independent directors to reject it.

AB InBev has already sweetened the approach twice - its opening salvo was worth £38 a share.

And it came out swinging after the latest refusal, noting that the new offer is 44% higher than where SABMiller shares were trading before takeover talk began swirling in September.

"How long will it be before shareholders see a value of over £42 in the absence of an offer from AB InBev?" asked Brito in his statement.

Related: 'Bud-Miller' would own nearly half the world's top beers

If AB InBev can complete its purchase of SABMiller, it would create a behemoth brewer that owns nearly half the world's top beers.

It would also be the largest takeover of the year, and among the biggest in history.

Shares in AB InBev were dipping by 1% Thursday, while shares in SABMiller were holding steady around £36.20 -- well below the bid level. That indicates investors have doubts that a deal will actually be sealed.