BEIRUT, Lebanon - A U.N. inquiry said on Monday Syrian cooperation with its investigation into the killing of a former Lebanese prime minister was slow and called on Damascus to arrest Syrian suspects.

"Given that its substantive lines of enquiry are far from being completed, and given the slow pace with which the Syrian authorities are beginning to discharge their commitments ... the commission recommends that there be such an extension and for a minimum period of six months," it said in a copy of the report to the Security Council obtained by Reuters in Beirut.

"Syria must detain those Syrian officials or individuals whom the commission considers as suspected of involvement in the planning, sponsoring, organizing or perpetrating of this terrorist act, and make them fully available to the commission."

The report said it had identified 19 suspects but did not name them. It said five Syrian officials questioned by U.N. investigators in Vienna this month were suspects.

It complained that Damascus was trying to cast doubt on the investigation's findings, and said it had asked to interview a sixth Syrian official, also considered a suspect, but that session had to be postponed.

"This was, at the least, an attempt to hinder the investigation internally and procedurally," it said.

The report said statements made by two of the Syrian suspects "indicated that all Syrian intelligence documents concerning Lebanon had been burned."

U.N. chief investigator Detlev Mehlis is due to present his findings at a U.N. Security Council meeting on Tuesday.

An interim report by Mehlis in October said the evidence pointed toward the involvement of Syrian officials and their Lebanese allies in Hariri's killing. Syria denies this.

On the basis of that report, the Security Council passed a resolution demanding that Syria fully cooperate with the probe or face unspecified action, which could lead to sanctions.

The new report comes hours after the assassination of Lebanese newspaper magnate and anti-Syrian lawmaker Gebran Tueni in a car bombing in Beirut.

Lebanese Prime Minister Fouad Siniora said he would ask the Security Council to look into a spree of bombings and assassinations that have rocked Lebanon in the past 14 months. (Reuters)