The US reportedly sent wooden pallets stacked with money aboard unmarked cargo plane to Tehran.

US Republicans are pushing new bills through Congress to prevent further return of Iranian money held since the Islamic Revolution in 1979.  
Those measures are in response to President Barack Obama's cash payments to Iran this year following a nuclear accord which requires Washington to lift its sanctions on Tehran.  
Iran reportedly received $400 million first in January and another $1.3 billion less than two months later. The total sum of $1.7 billion was related to an arms deal that Iran signed before 1979 but Washington was refusing to give back.  
Wooden pallets stacked with euros, Swiss francs and other currencies were reportedly flown into Iran in an unmarked cargo plane to cover the first $400 million, while the second payoff was likely made in cash since the US has no banking relationship with Tehran.
Republican lawmakers have now fielded new bills prohibiting any similar payments from the US, the country's media reports say.
A bill introduced by House Foreign Affairs Committee Chairman Ed Royce to ban future payments to Iran has reportedly attracted 36 co-sponsors and got a date squeezed into the body’s calendar for a vote.
In the Senate, Sen. Marco Rubio has introduced a similar measure which has attracted 20 co-sponsors in just three days, reports said.

Republican presidential candidate Sen. Marco Rubio gives a thumbs up to members of Congress. (Photo by Getty Images)

In a statement, Rubio hit out at Obama’s “misguided policies,” accusing him of attempting “to appease our enemy with pallets of cash secretly delivered on an unmarked cargo plane.”
The senator accused Iran of cheating on the nuclear deal even though the International Atomic Energy Agency (IAEA) once again confirmed Tehran's commitment to the accord in a report on Thursday.
Rubio's bill is reportedly competing with another being pushed by Sen. Bob Corker, the GOP chairman of the Senate Foreign Relations Committee.
Corker’s bill expands sanctions on Tehran over its ballistic missile program as well as Iran’s support for resistance groups such as Hezbollah. It also requires new sanctions for the transfer of conventional weapons to and from Iran, among other penalties.
According to weekly magazine the Washington Examiner, lawmakers know there's no chance that Obama will sign the bills into law in the waning days of his time in office but they want to force Democrats up for election in conservative states to take a tough vote on the measure.
The $1.7 billion returned to Iran constitutes a fraction of tens of billions of dollars of the Iranian assets which the US has blocked since the Islamic Revolution.
With the nuclear accord reached in February, US courts have scrambled through several cases, allowing American families to claim Iranian assets as compensation for a number of attacks which Tehran says have nothing to do with the country.
In April, the US Supreme Court ruled that Iran's $2 billion of assets held in an American bank be turned over to families of those killed in a 1983 bombing in Beirut and other attacks.
Foreign Minister Mohammad Javad Zarif denounced the move as “highway robbery” and pledged that Iran would retrieve the sum anyway. 

Secretary of State John Kerry (L) speaks with Iranian Foreign Minister Javad Zarif (R) in Vienna, July 14, 2015. (Photo by Reuters) 

Top Iranian authorities have also rebuked the US for “deception” on the nuclear accord and failing to fulfill its commitments. While Washington has to lift sanctions on Tehran under the accord, it has imposed even more penalties under numerous pretexts.
Last month, Deputy Petroleum Minister for trade and international affairs Amir Hossein Zamaninia said the US was terrorizing the Europeans into shunning business with Iran despite the lifting of sanctions.