The spending bill that US President Barack Obama signed this week includes a prohibition on the export of cluster bombs, which can kill for years after their use in wars. Cluster bombs spread small bomblets before impact, which greatly expands the kill zone. Many of the strewn weapons fail to explode until much later. Often they go off only after unsuspecting civilians pick them up. Democratic Senators Dianne Feinstein and Patrick Leahy have introduced further legislation that would ban not only the export of the weapons but their use by the US military. While the amendment to the spending bill, which Obama signed Wednesday, mentions no time limit for the ban, congressional aides said it probably would be considered permanent by the military.