(Edits, adds comment from U.S. official, paragraphs 6-7) WASHINGTON, Aug 13 (Reuters) - The United States said on Monday it had designated al Qaeda-inspired Fatah al-Islam, a militant group active in Lebanon, as a "terrorist" organization, subjecting it to U.S. financial sanctions. Over the last 12 weeks, Fatah al-Islam has been fighting the Lebanese army at the Nahr al-Bared Palestinian refugee camp in North Lebanon in clashes that have killed at least 278 people and displaced some 40,000 refugees. The group, which split from a Syrian-backed Palestinian faction last year, has Lebanese, Palestinians and other Arabs in its ranks, including some who have fought in Iraq. It says it supports al Qaeda's ideas but has no direct links. The State Department said the Secretary of State named Fatah al-Islam "as a Specially Designated Global Terrorist," a status that cuts the group off from the U.S. financial system. "As a result ... all property, and interests in property which Fatah al-Islam has in the U.S., or which enters the U.S. or comes under the control of U.S. persons, are blocked," the State Department said in a statement. The move may be partly symbolic. The U.S. goverment is not aware of Fatah al-Islam having any assets in the United States, said a U.S. official who asked not to be named. The official, however, said the goverment would only have a definitive picture once U.S. banks reviewed their accounts in compliance with the Fatah al-Islam's "terrorist" designation.