UN says some Syrian leaders suspected of war crimes

* Independent UN investigators issue report on Syria

* Document war crimes by both sides in conflict

* Say have list of suspects in "leadership positions"

* Call on Security Council to ensure accountability

By Stephanie Nebehay

GENEVA, Feb 18 (Reuters) - Syrians in "leadership positions" who may be responsible for war crimes have been identified, along with units accused of perpetrating them, United Nations investigators said on Monday.

Both government forces and armed rebels are committing war crimes, including killings and torture, spreading terror among civilians in a nearly two-year-old conflict, they said.

The investigators' latest report, covering the six months to mid-January, was based on 445 interviews conducted abroad with victims and witnesses, as they have not been allowed into Syria.

The independent team, led by Brazilian Paulo Pinheiro, called on the U.N. Security Council to "act urgently to ensure accountability" for grave violations, possibly by referring the violators to the International Criminal Court for prosecution.

"The ICC is the appropriate institution for the fight against impunity in Syria. As an established, broadly supported structure, it could immediately initiate investigations against authors of serious crimes in Syria," the 131-page report said.

It added: "Individuals may also bear criminal responsibility for perpetuating the crimes identified in the present report. Where possible, individuals in leadership positions who may be responsible were identified alongside those who physically carried out the acts." (Reporting by Stephanie Nebehay; Editing by Alistair Lyon)