(Reuters) - Dish Network Corp on Monday said it was still doing due diligence on Sprint Nextel Corp , for which it made an unsolicited $25 billion offer in April.

Sprint shareholders were due to vote on Wednesday on SoftBank Corp's deal to buy 70 percent of Sprint. Dish said it was still in the process of negotiating the terms of an agreement of its own with Sprint.

Dish has been taking a closer look at Sprint's books for the last few weeks as it had said that its offer was subject to the completion of a due diligence process.

Dish reiterated in a statement on Monday that it believed its proposal "is both economically and strategically superior to that of SoftBank".

Speculation has swirled that Sprint's board may consider delaying the shareholder vote on the SoftBank deal as it was waiting for a binding offer from Dish.

Sprint declined to comment.

(Reporting by Ben Berkowitz and Nicola Leske; Editing by Maureen Bavdek and Carol Bishopric)

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