(Reuters) - Syria's conflict will cost Lebanon $7.5 billion in cumulative economic losses by the end of next year, the World Bank has said in a report prepared for an aid meeting at the United Nations.

A summary of the report, seen by Reuters after the World Bank briefed diplomats in Beirut, provides the most detailed assessment yet of the strain Syria's conflict has placed on its small Mediterranean neighbor.

It estimates that the war and resulting wave of refugees into Lebanon will cut real GDP growth by 2.85 percent a year between 2012 to 2014, double unemployment to above 20 percent and widen the deeply indebted nation's deficit by $2.6 billion.

U.S. ambassador to Lebanon David Hale said on Thursday the bank's assessment underscored just how serious a challenge Lebanon faces, and the importance of dealing with it "not only for humanitarian reasons, but for Lebanon's very stability".

The Syrian war has spilled into Lebanon with car bombs in Beirut and Tripoli, street fighting in major cities and rocket fire in the Bekaa Valley. [Link]