Clorox Co (CLX.N) once again turned down an offer from activist investor Carl Icahn, calling his latest bid of $80 per share "inadequate."

The bleach maker's board unanimously decided that Icahn's offer, which came after Clorox swiftly rejected his initial bid of $76.50 per share, "substantially undervalues the company and is not credible," Clorox said in a statement on Tuesday.

Icahn, Clorox's largest shareholder, could not be immediately reached for comment.

Icahn's latest offer, announced on July 20, values Clorox at $10.66 billion, plus the assumption of debt.

Clorox said that it remains open to considering any "credible plan" to create significant value for its shareholders.

"Our board has carefully considered Mr. Icahn's revised proposal and concluded that it is inadequate and unlikely to be completed," lead director Gary Michael said in a statement. "The board also believes Mr. Icahn's revised proposal lacks detail and contains significant conditionality."

Last week, Icahn offered to put $6.2 billion, including his Clorox shares, into escrow "to put the question of credibility to rest once and for all.

Icahn's bid of $80 per share values Clorox at $10.66 billion, based on roughly 133.3 million shares outstanding as of March 31. Excluding the 12.5 million shares Icahn owns, he would pay about $9.66 billion for the rest of Clorox's shares and would also assume $2.125 billion in long-term debt.

Icahn said last week that he did not believe there was any legitimate question about whether he could raise the additional $7.8 billion for the offer on top of his $5.2 billion in shares.

Icahn made his first offer for Clorox public on July 15, and at that time suggested that some of Clorox's rivals should swoop in to buy the company for more than he was offering. So far, no other buyers have stepped up to buy Clorox, which is best known for its namesake bleach.

Shares of Clorox rose to $73.49 in after-hours trading.