Iranian officials increased their defense budget but "exactly the same amount" as the recently-negotiated U.S. settlement payment, according to a trio of GOP senators who want President Obama's team to explain a shipment of cash to the country that was widely viewed as a ransom for several American hostages.

President Obama agreed to send $1.7 billion to Iran, thereby ending a decades-old dispute over repaying the regime for money spent purchasing weapons that were never delivered because of the 1979 revolution. The deal was announced in January, just as Iran released five American hostages. That coincidence raised suspicions on Capitol Hill immediately that the $1.7 billion functioned as a ransom payment, a concern exacerbated by new reports that the Obama administration had $400 million in cash flown into the country before the hostages were released.

"Iran has increased its defense budget by $1.7 billion — exactly the same amount as the U.S. settlement payment," Georgia Republican Sens. David Perdue and Johnny Isakson, along with Illinois Republican Mark Kirk, wrote in an Aug. 8 letter to Secretary of State John Kerry. "Can you confirm that this is true? Does this not indicate to you that Iran is expanding its military and nefarious operations at the expense of the U.S. taxpayer?"

Iran's use of that money was first reported by Saeed Ghasseminejad, at the Foundation for Defense of Democracies, who noted that it was part of an overall $19 billion increase in Iranian military spending. "The budget allows $19 billion to go to the military establishment – the Islamic Revolutionary Guard Corps (IRGC), regular military, and Defense Ministry — a 90 percent increase in military spending compared to the previous year," Ghasseminejad wrote in June.

The senators asked Kerry to explain if he has "any monitoring systems in place" to ensure that the cash payment isn't used to fund terrorism and they faulted the Obama administration for agreeing to make "any settlement payments" to the regime. "Iran owes American victims of terrorism $46 billion," they noted. "Why would the administration pay Iran $1.7 billon when Iran owes American victims so much more? What efforts is the administration making to ensure that these American victims and their families receive damages that Iran owes them?"