Seventeen senators have set up a congressional inquiry, led by GOP Sens. Kelly Ayotte of New Hampshire and Ted Cruz of Texas, to analyze Iran's military activity since the nuclear agreement with the country went into effect.

According to The Washington Free Beacon, some of the $1.7 billion cash payment the U.S. made to Iran may have been used to help Yemeni terrorists, who fired missiles on a U.S. Navy ship in the Red Sea.

Lawmakers suspect that a large part of the $1.7 billion, which critics have said went to Iran as ransom for hostages, is being used to support Iran's terror operations and its military.

"Just this weekend, Iranian-backed Houthi rebels shot missiles at a U.S. Navy destroyer in the Red Sea. It is not a coincidence that Iranian aggression against America and our allies has doubled since the JCPOA went into effect — the $150 billion signing bonus is clearly going a long way," Cruz said, referring to the Iran trade deal.

President Barack Obama's administration did not inform officials about the delivery of the cash to Iran, Cruz added, and "Congress has an obligation to ensure President Obama's willful blindness towards the very real threats we face does not further endanger the American people."

In the letter, the senators wrote that Iran is "almost certainly using this windfall to skirt the arms embargo and illicitly purchase weapons for the Islamic Revolutionary Guard (IRGC), the terrorist organization Hezbollah, and/or the murderous Assad regime in Syria."

"We are deeply concerned that this large infusion of U.S. taxpayer-funded cash into the coffers of the world's leading state sponsor of terrorism is going to further embolden Iran and result in our troops and our allies confronting more lethal and better equipped adversaries and potential adversaries," the senators said in the letter.

The lawmakers called for an official assessment on Iran's military behavior and terror financing since the U.S. sent the payment and they want to know if "correlation between the increased financial resources now available to Iran and the increase in its belligerent activities," the letter said.

An opinion column in The Wall Street Journal said the deal has emboldened Iran, not made them more willing to work with the U.S.

"The Administration grants the mullahs unprecedented concessions not called for by the nuclear deal, and they respond by attacking the U.S. Maybe President Obama sees a foreign-policy paradox at work. A better way of describing the dynamic might be cause-and-effect."