– A secret U.S. intelligence assessment predicts that Iran's government will pump most of an expected $100 billion windfall from the lifting of international sanctions into the country's flagging economy and won't significantly boost funding for terrorist groups and sectarian militias it supports in the Middle East.

Intelligence officials have concluded that even if Tehran increases support for Hezbollah commanders in Lebanon, Houthi rebels in Yemen or President Bashar Assad's embattled government in Syria, the extra cash is unlikely to tip the balance of power in the world's most volatile region, said two U.S. officials who spoke on condition of anonymity to discuss the intelligence document.

The controversial CIA report, which has been briefed to key members of Congress, thus provides ammunition to both sides in the battle brewing on Capitol Hill over President Obama's signature foreign policy achievement, a sweeping deal to block Iran's ability to build nuclear weapons for at least a decade in exchange for the easing of sanctions that have hobbled the country's economy.

Under the deal sealed Tuesday in Vienna, once Iran completes a series of strict requirements, the U.S., the European Union and the United Nations will suspend the most damaging sanctions against Iran's financial and energy sectors, and Tehran will be given access to about $100 billion from oil revenue frozen in overseas accounts. That could occur in early 2016.

The United States also will rescind most of its banking sanctions, allowing Iranian banks to reconnect to the global financial system, and will lift restrictions on Iran's automotive, shipping and insurance industries, as well as on trade in gold and precious metals. In all, 444 companies or individuals, 76 aircraft and 227 ships would be removed from U.S. blacklists.

Non-nuclear sanctions, including those related to human rights abuses and Iran's support for terrorism, will remain in place. A U.N. arms embargo would lift in five years.

Republican lawmakers seized on the conclusion that Iran could increase support for terrorist groups and expand its military role in Yemen, Syria and other regional hot spots, describing it as a fatal flaw in the Vienna agreement.

Lawmakers have 60 days to review the accord and an option to approve or reject it. Opposition is widespread among Republicans, but it's far from clear whether they can secure enough votes to override a promised White House veto.