The U.N. report called on the Damascus government to arrest Syrian officials and others suspected of involvement.
The report, from lead U.N. investigator Detlev Mehlis, failed to name the 19, but said five Syrian officials questioned earlier in December in Vienna were among the suspects.
"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.
Monday's report follows interim findings released in October that pointed to top Syrian and Lebanese security officials, among them relatives of Syrian President Bashar Assad, as suspects in the case. The new report said new evidence had reinforced the earlier findings.
In the report, Mehlis who is scheduled to present his findings to the U.N. Security Council on Tuesday, said Syria had tried to stall the investigation by failing to allow the interrogation of a sixth suspect in Vienna.
"This was, at the least, an attempt to hinder the investigation internally and procedurally," the document said.
The report also called for an extension of the investigation beyond Mehlis' tenure. The German prosecutor is due to end his six-month term following the Security Council meeting.
"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."
Syria has denied any involvement in Hariri's death and recently allowed U.N. investigators to question Syrian nationals in Vienna. The report said that two of the Syrians questioned in the Austrian capital "indicated that all Syrian intelligence documents concerning Lebanon had been burned," according to Reuters.
Syria has the Mehlis report and is studying it, a Syrian official who asked not to be identified, told Reuters.
The report, which could help determine if the Security Council will choose to take further action against Syria in the investigation, came the same day a car bomb explosion in Beirut killed the anti-Syrian publisher of the country's An-Nahar newspaper Gebran Tueni and four others.
Tueni had on Sunday arrived in Lebanon from Paris where he had spent the last several months in fear of assassination, according to Reuters.
Lebanese officials blamed Syria, which again denied any role, for the attack. A group calling itself "Strugglers for the Unity and Freedom of the Levant" claimed responsibility. Investigators said the wording of the claim seemed designed to implicate Syria, Reuters reported.