MANILA, March 19 (Reuters) - Philippine troops may re-position on a remote southern island where they have encircled Islamic rebels holding three Red Cross workers captive, officials said on Thursday.

The leader of the Abu Sayyaf rebels holding the three officers threatened on Wednesday to behead one of the hostages if troops did not stop pursuing them.

"We will not pull out, only we will re-position our troops as necessary to allow the exhaustion of other peaceful means for the safe release of the victims," said a military statement.

Military chief General Alexander Yano, however, said no such orders had yet been given.

"If that is warranted on the ground to allow a peaceful resolution then maybe that can be one of the options available, but there has been no order yet and there is no such movement that is being undertaken," he told reporters.

"The primary objective is to safely recover the hostages."

Senator Richard Gordon, the head of the Philippine Red Cross who has been in contact with the kidnappers, told television that one of the hostages could be released if the troops pulled back.

"One of our staff can get out as soon as they pull out," he said.

"I am now talking with the military so we could know when we could tell (the kidnappers) that the military can start moving out so that we can immediately make a plan to pick up the person who's going to be taken out."

At least three soldiers and up to six rebels were killed, and dozens injured, in exchanges of gunfire between marines and the kidnappers on Monday and Tuesday. Gordon has said the hostages were not harmed.

The International Committee of the Red Cross (ICRC) hostages -- Swiss national Andreas Notter, Italian Eugenio Vagni and Filipina Mary Jean Lacaba -- have been held on the island of Jolo since Jan. 15.

The Abu Sayyaf rebels, notorious for kidnappings and linked to Southeast Asian Islamist group Jemaah Islamiah, have a history of beheading captives.

In June 2001, American Guillermo Sobero was beheaded by Abu Sayyaf on Basilan island, near Jolo, after Manila turned down talks on the release of three U.S. captives.

The Abu Sayyaf has demanded the withdrawal of the military from their areas in exchange for freeing the Red Cross captives.

Newspapers have said they have also demanded a ransom, with one estimate put at $1 million. (Reporting by Manny Mogato; Editing by Jerry Norton)

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