By Greg Roumeliotis

(Reuters) - Monsanto Co <MON.N>, the world's largest seed company, has still not opened its books more than two weeks after it rejected Bayer AG's <BAYGn.DE> $62 billion acquisition offer but left the door open to a possible deal, according to people familiar with the matter.

The impasse shows that little progress in negotiations has been made since Monsanto on May 24 turned down its German peer's $122-per-share cash offer but said it was open to "continued and constructive conversations."

Monsanto has said that Bayer's offer "significantly undervalues (the) company and also does not adequately address or provide reassurance for some of the potential financing and regulatory execution risks related to the acquisition."

Bayer, however, has no plans to increase its offer without first reviewing Monsanto's confidential information, the sources said on condition of anonymity because of the confidentiality of the talks.

The Leverkusen-based company needs access to Monsanto's books before it can decide whether it can pay a higher price, as well as offer a more detailed plan on how to address potential antitrust risks, the sources added.

Bayer also has no intention currently to go hostile with its bid, the sources said.

Monsanto, based in St. Louis, has not directly told Bayer that it is looking for better terms in order for it to offer the German company access to confidential information, according to one of the sources.

However, Monsanto's lack of engagement demonstrates that it not only views Bayer's offer as too low, but that it does not even consider it as a basis for negotiations, the sources said.

The situation did not change even after Monsanto held a regular board meeting this week to approve a quarterly dividend of 54 cents per share.

Bayer declined to comment, while a Monsanto spokeswoman did not respond to a request for comment.

The Wall Street Journal had reported earlier on Friday that Bayer had made a new takeover approach to Monsanto that was rebuffed, in part because it didn't include a higher price.

Bayer's unsolicited bid for Monsanto is the largest all-cash takeover on record, according to Thomson Reuters data, just ahead of InBev SA's $60.4 billion offer for Anheuser-Busch in June 2008.

Global agrochemicals companies are racing to consolidate, partly in response to a drop in commodity prices that has hit farm incomes. Seeds and pesticides markets are also increasingly converging.

ChemChina plans to buy Switzerland's Syngenta <SYNN.S> for $43 billion, after Syngenta rejected a bid from Monsanto. Dow Chemical Co <DOW.N> and DuPont <DD.N> are forging a $130 billion business.

(Reporting by Greg Roumeliotis in New York; Additional reporting by Arno Schuetz and PJ Huffstutter in Chicago; Editing by Paul Simao)