Ackman, whose hedge fund Pershing Square Capital Management is Allergan’s biggest shareholder, told reporters that his lawyers had seen documents that show Allergan’s board knowingly released misleading statements about Valeant.

"We've actually found evidence that will come out in the next few days of attempts at manipulating Valeant's stock price down," Ackman said, noting that he has not seen that evidence because it has been marked as "highly confidential."

Allergan and Valeant had no immediate comment and Reuters could not independently verify Ackman's claim. Allergan executives have previously said the concerns they expressed about Valeant were based on their knowledge of the Canadian company and the industry.

In an unusual alliance, even by hedge fund industry standards, Ackman has been working with Valeant for months to push the Botox maker into selling itself to Valeant. Allergan has steadfastly refused, calling Valeant’s offer too low and looking for other partners to avoid a deal with Valeant.

"We believe they put those statements out, that they knew that they were false at the time they made them, and we have found evidence to that effect, that this was a conscious takeover defense strategy to malign Valeant and the company," Ackman said after speaking at a conference.

Pershing Square is expected to file court documents early next week related to Allergan's lawsuit, which accuses the hedge fund and Valeant of breaking insider trading rules, said a person familiar with the matter but not authorized to discuss it publicly.

It is not clear if those court documents will include the material that Ackman says exists about the Allergan board's alleged misleading of investors.

"I think it will come to light in the context of litigation," Ackman said, giving only a vague hint of when the material will be made public.

Sources familiar with Valeant and Pershing Square have hinted that the company might be willing to raise its bid for Allergan, possibly as soon as next week when Valeant is expected to release earnings which the company has signaled will be strong.

Ackman has lined up a list of other big investors who have called on Allergan to call a special meeting in December where the hedge fund manager is expected to try and replace Allergan board members with his own directors who might be more receptive to Valeant's overtures.

As the battle for Allergan drags on each side has ratcheted up the rhetoric.

In a letter to the Allergan board in September, Ackman accused them of having libeled Valeant and said he had complained to U.S. and Canadian regulators.

Separately, last month Valeant Chief Executive Officer Michael Pearson wrote to Allergan alleging that it was making "baseless attacks" about his company. Allergan Chief Executive David Pyott and lead independent director Michael Gallagher said at the time that the company relied on its knowledge of Valeant and of the industry to express concerns about Valeant's business model.

Known for making big bets on companies including Canadian Pacific and General Growth Properties, Ackman has also relied on the media to press his points.

(Reporting by Alastair Sharp and Allison Martell, writing by Svea Herbst-Bayliss; Editing by Jeffrey Hodgson and Chizu Nomiyama)

By Alastair Sharp and Allison Martell