London, president of Hudson until 2011, said the State Department has ignored non-Brotherhood opposition groups. In July, Secretary of State Hillary Clinton invited Brotherhood operatives and urged them to work with Turkey to help oust Assad.

"Missing from the invitations are Kurdish leaders, Sunni liberals, Assyrians and Christian spokesmen," the report said. "According to various reports the State Department made a deal with Turkey and Muslim Brotherhood representatives either to share power with Assad to stabilize the government, or replace him if this effort fails."

Hudson cited the Syrian Democracy Council, which contains a range of ethnic and religious minorities, including Alawites and Christians. SDC was not invited to the State Department.

"From the standpoint of Foggy Bottom [State Department] it is far better to promote stability even if this means aligning oneself with the goals of presumptive enemies," the report said. "This, however, is a dangerous game that not only holds U.S. interests hostage to the Muslim Brotherhood, but also suggests that the withdrawal of American forces from the region affords the U.S. very few policy options."

Officials confirmed the State Department invitation to Brotherhood-aligned opposition groups. They said the Brotherhood has often boycotted U.S.-sponsored sessions that included organizations opposed by the Islamist movement.

London said the U.S. ban on SDC represented an insult to pro-democracy forces in Syria. He cited reports that the Brotherhood was playing a major role in attacks on Syrian security forces in a campaign supported by Iran, Jordan and Turkey.

"At the very least Secretary Clinton should hear the SDC argument," the report said. "Leaving this body out of the Syrian conversation is an insult to what America purports to care about. Assad should see that his opponents are not merely those complicit in stabilizing a murderous regime, but those with genuine democratic impulses and who represent a significant portion of the Syrian people."