NEW YORK - NRG Energy said on Wednesday it has expended an enormous amount of time and resources considering Exelon Corp's unsolicited takeover offer and it continues to view it as inadequate.

We would support a deal with Exelon at a fair price but, at this point, we have no reason to believe they are willing to offer a fair price, said NRG, in an open letter to its shareholders.

In October, Exelon, the largest U.S. nuclear power company, made an unsolicited offer to buy NRG for $6.2 billion. NRG said the offer was too low, prompting Exelon to bypass NRG's management and make a tender offer directly to shareholders.

Under the offer, NRG shareholders have tendered 106.3 million shares, or about 45.6 percent, of NRG common stock outstanding, Exelon said last month.

Exelon extended the exchange offer to February 25. It was previously scheduled to close on January 6. Exelon has offered to acquire NRG at a fixed price of 0.485 shares of Exelon common stock for each share of NRG common stock.

Exelon has also nominated a slate of directors for NRG's board, as it raises the pressure in its hostile bid for the independent power producer.

NRG said it has held discussions with Exelon Chief Executive John Rowe, but these discussions have proven to be fruitless.

Rowe made it clear that Exelon would not make any meaningful increase in the price being offered to NRG stockholders, even if allowed to conduct due diligence, said NRG.

NRG, in its letter, urged shareholders that have already tendered shares toward the offer to retract their tender, so as to prompt Exelon to raise its offer.

(Reporting by Euan Rocha, editing by Dave Zimmerman)