WALNUT CREEK, Calif. — Drug store chain Longs Drug Stores Corp. said Thursday the Federal Trade Commission has asked it to provide documents in connection with a proposed takeover by Walgreen Co.

The company said the FTC is investigating whether an acquisition will "substantially lessen competition" among retail pharmacies in parts of California, Nevada and Hawai'i.

Longs said the FTC has requested information about its operations in Hawai'i and its mail-order business.

The company said it will cooperate in the FTC's investigation.

Walgreen has offered to buy Longs for $75 per share, or $2.8 billion. Longs, though, has already accepted CVS Caremark Corp.'s lower bid of $71.50 per share, or $2.7 billion. That deal has already been approved by regulators.

In a statement, CVS said the FTC's investigation highlights the antitrust risk in a proposed Walgreen-Longs bid, and said any deal between the companies could face long delays due to regulatory review.

"Walgreens has the second largest number of pharmacy counters in Northern California (Longs has the most) and has announced plans to aggressively enter Hawai'i (where Longs is by far the largest and strongest pharmacy operator)," the company said.

Shares of CVS rose $1.09, or 3.3 percent, to $34.19 while Longs shares added 17 cents to $76.26 in midday trading. Walgreens shares gained 61 cents to $32.23.