Congress is warning that billions of dollars in U.S. arms sales to Qatar could be enabling the Arab country’s support for leading terrorist organizations and allies, according to a letter to the administration being circulated on Capitol Hill.

Qatar, long one of America’s top Arab military allies in the Middle East, has been funding and providing refuge to an increasing number of terrorist groups and allies in recent years, including most recently the Islamic State (IS).

The United States sends billions of dollars and arms to Qatar to keep it as a strategic regional ally.

Congress’ concern about Qatar’s support for the terror group comes ahead of a high-profile meeting between the country’s ruling emir, Sheikh Tamim bin Hamad al Thani, and President Barack Obama at the White House on Tuesday.

The letter, which is being circulated Rep. Doug Lamborn (R., Colo.), a member of the House Armed Services Committee, calls out Qatar for being "the world’s safe haven for terrorist groups and militia leaders." It urges U.S. officials to "reassess and reevaluate" America’s multi-billion dollar military alliance with the country.

The sharp focus on Qatar, a key military ally that receives billions in arms from the United States, come as the country faces increased scrutiny over an uptick in support for radical jihadist groups plotting against the West.

The lawmakers say the billions in U.S. assistance to Qatar could be enabling terror regimes there to thrive.

"America’s military footprint in Qatar may be enabling the Al Thani regime to offer up its territory as a fundraising center for terrorists around the region," states the letter addressed to newly installed Defense Secretary Ashton Carter, according to an advance copy obtained by the Washington Free Beacon. "The past few years have seen Qatar grow into a major hub for terrorist operatives and terrorism finance."

Qatar claims to support America’s campaign against Islamic State (IS) terrorists, yet does little to help the cause, the lawmakers say.

"The Qatari government turns a blind eye to terrorist fundraising for al Qaeda and the Islamic State by U.S.-designated persons within its borders," the letter states.

"The Qatari government has also actively financed, advocated for, and—at least until recently—hosted the Palestinian terrorist group Hamas, a relationship that Doha is only being compelled to reconsider after increased pressure from other Gulf States, not the United States."

"Further evidence suggests that Qatar has directly armed or financed multiple Islamist groups in the region, undermining U.S. objectives in pivotal countries such as Libya, Egypt, and Syria by pushing those places toward violent extremism," the letter states.

Key leaders of the Muslim Brotherhood and Taliban also have "found a safe haven in Qatar," where they have free rein to "safely coordinate radical activities and in some cases even terrorism in the region without interruption," according to the letter.

As Qatar accommodates and funds terror groups such as Hamas, IS, and al Qaeda, it simultaneously cashes in on massive U.S. arms deals. The lawmakers maintain that this U.S. money only emboldens the Qatari government.

"U.S. reliance on Qatar’s support such as the Al Udeid base in Qatar has emboldened the Qataris to believe they can undermine and damage American interests and efforts in the region without consequence," they write. "America's strategic interests should not be undercut or held captive."

"Bahrain, Kuwait, Jordan, and the [United Arab Emirates] all have advanced bases which can support the same U.S. aircraft and facilities, possibly making the need for such an extensive installation in Qatar redundant," they propose.

The lawmakers urge Carter and the Defense Department to begin developing "a strategy to hold Qatar accountable for their support of terrorism, including a serious exploration of positioning some of our military assets with other allies in the region."

On Tuesday, Obama will host Qatari Emir al Thani at the White House.

"The president looks forward to discussing with Sheikh Tamim political, economic, and security issues of mutual concern to our two countries," it said in a statement. "The United States and Qatar have a long-standing partnership and this meeting is an opportunity to further that relationship along with our shared interest in supporting stability and prosperity in the Middle East."