(Recasts throughout with Abbas comments, adds Haniyeh)

By Niklas Pollard

STOCKHOLM, April 19 (Reuters) - Palestinian President Mahmoud Abbas said on Thursday he was convinced a BBC journalist abducted in Gaza last month was still alive despite an Islamist group's claim to have killed him.

Abbas said while on a visit to Sweden that the abductors of BBC reporter Alan Johnston had been identified, though the Palestinian Authority had not been in contact with the group.

An e-mail in the name of the Tawhid and Jihad Brigades sent to media outlets on Sunday said the group had killed Johnston, one of the few Western reporters based in Gaza, and would release a video of his killing later.

"Our intelligence services have confirmed to me that he is alive," Abbas told a news conference through an interpreter.

"I want to acquire his release alive. Therefore it is taking some time."

Separately, Palestinian Prime Minister Ismail Haniyeh of Hamas told Dutch television station RTL-4 that Johnston's captors did not have political motives but rather wanted "personal demands" met in exchange for the journalist.

Haniyeh did not offer any details about what these demands might entail and said the British government had made clear to the Palestinian Authority that it should not use force to free Johnston because that could endanger his life.

Top Palestinian negotiator Saeb Erekat, who accompanied Abbas to Stockholm and interpreted for him, told Reuters authorities were working to secure the freedom of the BBC reporter who disappeared on March 12.

"The president is reassured that he is alive and every effort is being exerted now to acquire his release," he said.

Abbas, whose Swedish visit was part of a diplomatic push to encourage the European Union to unlock financial aid to the Palestinian government, said he had been briefed about Johnston over the past three days.

"This does not mean that we have any contact with his abductors," he said. "(But) we know this group."

"We know these people and we want Johnston safe and I think the less we talk about it the more we provide for his safety."

Abbas would not confirm if the hitherto unknown Tawhid and Jihad Brigades were holding the journalist. The BBC said last week Abbas had told it he had evidence Johnston was alive.

The e-mail sent on Sunday claimed Johnston had been killed after Palestinian and British authorities failed to meet demands for prisoners to be freed from Israeli jails.

However, no such demand has been made public since Johnston vanished.

Erekat said he was not aware of Palestinian authorities receiving any demands related to the abducted journalist.

(additional reporting by Jerusalem bureau)

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