A classified memo sent by Mrs. Clinton last December made it clear that residents of Saudi Arabia and its neighbors, all allies of the United States, are the chief financial supporters of many extremist activities. “It has been an ongoing challenge to persuade Saudi officials to treat terrorist financing emanating from Saudi Arabia as a strategic priority,” the cable said, concluding that “donors in Saudi Arabia constitute the most significant source of funding to Sunni terrorist groups worldwide.”

The dispatch and others offered similarly grim views about the United Arab Emirates (“a strategic gap” that terrorists can exploit), Qatar (“the worst in the region” on counterterrorism) and Kuwait (“a key transit point”). The cable stressed the need to “generate the political will necessary” to block money to terrorist networks — groups that she said were “threatening stability in Pakistan and Afghanistan and targeting coalition soldiers.”…

While federal officials can point to some successes — prosecutions, seizures of money and tightened money-laundering regulations in foreign countries — the results have often been frustrating, the cables show. As the United States has pushed for more aggressive crackdowns on suspected supporters of terrorism, foreign leaders have pushed back. In private meetings, they have accused American officials of heavy-handedness and of presenting thin evidence of wrongdoing by Arab charities or individuals, according to numerous State Department cables.