Jerusalem, Jan 8 (IANS): An audio recording, in which Israel's Prime Minister Benjamin Netanyahu is heard negotiating mutual benefits with a businessman, has been obtained and included in the criminal investigation against the leader, authorities said on Sunday.

The investigation into the allegations of corruption contained a tape, in which an unidentified businessman offers to help Netanyahu remain in office in exchange for financial benefits and favours, Efe news reported.

The taped evidence would be included in one of the two cases being investigated by the police since last year, known as "Case 2,000".

Netanyahu has been subjected to two police interrogations in a week. The first one lasted for three hours over the alleged irregular receiving of valuable gifts; and the second for five hours, relating to an attempt to receive a bribe.

Israeli President Reuven Rivlin was surprised "by the evidence" that the police produced during the interrogations, sources close to Netanyahu said.

Netanyahu has admitted to receiving gifts, but maintained that this is normal between friends, and denied having committed any irregularities.