(AFP) A potential Malaysian mediator today voiced shock at claims by Abu Sayyaf rebels in the southern Philippines that they had beheaded an American hostage.

Businessman Yusuf Hamdan said that if the claim were true he and another Malaysian, politician Sairin Karno, would not mediate in the hostage crisis as the Muslim rebels have demanded.

"I was very upset when I heard the news," Yusuf told AFP . "I have asked the Radio Mindanao Network to relay a message to the Abu Sayyaf group to call me to confirm the news."

A spokesman for the Abu Sayyaf kidnappers told the radio station that Californian Guillermo Sobrero had been killed because President Gloria Arroyo refused to call off military operations against the rebels.

There was no immediate independent confirmation of the claim.

"How can we mediate when you (Abu Sayyaf) do not give us a chance to talk. Why should we go if they do not honour their words," Yusuf said.

Yesterday Yusuf said he had spoken to Abu Sayyaf spokesman Abu Sabaya by mobile phone and told him not to carry out his threat to behead three US captives.

"I told him it is an inhuman act. Please, as Muslims it is against our religion to do it."

Arroyo bowed to pressure

Arroyo had bowed to the Abu Sayyaf demand for the Malaysian mediators. Her spokesman had said Manila would contact the government in Kuala Lumpur.

Prime Minister Mahathir Mohamad told reporters Tuesday he had not yet received any formal request from Arroyo. "We will study it (the request)," he said.

The two Malaysians had said they were willing to mediate but not without the approval of their own government.

Last year the Malaysians, both from the eastern state of Sabah, helped negotiate the release of dozens of captives - foreigners and Malaysians - who were abducted by the Abu Sayyaf rebels.

Yusuf said they were concerned about their own safety now. "Next time they will chop off our heads."

Sairin is a former member of Malaysia's upper house of parliament and a local chief in Sabah of the ruling United Malays National Organisation.

The Abu Sayyaf gunmen say they are fighting for an independent Islamic state in the southern Philippines, but are known mainly for kidnappings for ransom.