BOSTON, Oct 20 (Reuters) - Billionaire investor William Ackman, whose fund is the largest shareholder in Allergan Inc. , and Valeant Pharmaceuticals said the botox maker's Chief Executive Officer David Pyott tried to discredit Valeant as it was making a hostile takeover bid, court documents showed.

The court filing made late on Monday in California further raises the tensions between the two sides in a deal that could become the year's biggest if it is completed.

Ackman's hedge fund has been working with Valeant for months to craft a deal for Valeant to buy Allergan, but Allergan has rejected all of Valeant's overtures and tried to find other potential partners to avoid a deal.

In the filing with the federal court in Santa Ana, California, lawyers said that Pyott provided false and misleading information about Valeant to investors, failed to disclose Allergan CFO Jeff Edward's resignation in a timely manner, and ignored outside advisors' input when he falsely called Valeant's account "opaque" and "problematic."

A spokesman for Allergan was not immediately available for comment.

The case is Allergan Inc et al v. Valeant Pharmaceuticals International Inc et al, United States District Court Central District of California Southern Division - Santa Ana No. 14-01214

(Reporting by Svea Herbst-Bayliss; Editing by Miral Fahmy)