MONTREAL -- Valeant Pharmaceuticals says that it's prepared to "improve" its takeover offer for Allergan Inc. and "provide value" of at least US$200 a share to shareholders of the California-based maker of Botox.

That would be about US$21 per share higher than the value of Valeant's offer as of Friday.

Valeant's letter doesn't spell out what combination of cash and stock that it would would be prepared to offer but the letter suggests part of the increase would be due to a higher valuation for its own shares.

Valeant previously offered US$72 in cash plus 0.83 of a Valeant share in June -- about US$179 based on Friday's closing stock prices but Allergan has rejected the bid.

"To be clear, Valeant is prepared to improve its offer and provide value to your shareholders of at least $200 a share. We are confident that an increase in our stock price, and in consideration, will provide that value. No other potential acquirer of Allergan has the operational and tax synergies that we have, and no other potential acquirer of Allergan can provide the value that we can," Valeant chairman and CEO Michael Pearson said in the letter.

Valeant shares closed Friday at US$129.13 on the New York Stock Exchange and at C$145.21 on the Toronto Stock Exchange.

Allergan's stock closed at US$184.21 on Friday but rose to about US$190 in pre-market trade after Valeant released the letter through a media statement.

Valeant, a multinational pharmaceutical company based in Laval near Montreal, said in the letter that its own share price has been trading at "artificially low" values and accuses Allergan's management of "baseless attacks and frivolous litigation."

The company has partnered with Allergan's largest shareholder, activist investor Bill Ackman and his investment firm Pershing Square Capital Management LP.

Valeant and Pershing Square are also in a number of related battles with Allergan, including claims and counterclaims filed by the companies in a U.S. district court in California and an attempt by Pershing Square to oust members of the Allergan board through a shareholder vote next month.