US military experts have been advising Filipino forces
The Abu Sayyaf have offered to negotiate over the release of two Americans and about nine Filipinos they are holding on the southern island of Basilan.
But the military has been making gains since an all-out offensive began in July, with several arrests - and clashes this week in which nine rebels were killed.
The faction holding American Christian missionary couple Martin and Gracia Burnham is still in hiding.
The body of a third American kidnapped with them in May, Guillermo Sobero, was found beheaded last month.
More than a dozen Filipino hostages have been killed.
'No conditions'
On Friday a top Philippines military chief said calls for talks by Abu Sabaya, spokesman of the Abu Sayyaf, could be a "diversionary tactic".
"Just surrender and release the hostages," said southern military chief Lieutenant General Roy Cimatu.
"We will not allow him to trick our troops so even if there is a pronouncement like this, we will still continue our operations."
The Abu Sayyaf group says it is fighting for an independent homeland in the south of the predominantly Catholic country but its main activity has been kidnap for ransom.
The government has repeatedly ruled out negotiating with the group, though it is holding peace talks with another rebel group currently on ceasefire, the Moro Islamic Liberation Front (MILF).
"The military and the government will not agree to have conditions", National Security Adviser Roilo Golez reaffirmed on Friday.
US help
He said the Abu Sayyaf's fighters may have fallen to less than 800, from an estimated 1,000 early this year.
The military said on Thursday it had received a letter supposedly sent from the rebels in which Martin and Gracia Burnham asked for food and other items.
Officials said the letter was delivered to a marine brigade on Basilan, 900 kilometres (560 miles) south of the capital Manila.
On Thursday they could not confirm its authenticity.
A team of 23 US military advisers is expected to meet top military officials in Manila. They have spent the last week in the southern Philippines assessing the needs of the armed forces in their offensive against the Abu Sayyaf.