WASHINGTON (AP) — Republican lawmakers are calling for Iran to be expelled from the main financial system that oversees international bank transfers, as the Trump administration steadily re-imposes sanctions on the country following the U.S. withdrawal from the Iran nuclear deal.

A group of 16 GOP senators led by Ted Cruz of Texas urged Treasury Secretary Stephen Mnuchin on Thursday to take "all necessary steps" to disconnect Iran from the SWIFT network, which allows financial institutions to send and receive information about banking transactions.

"Quick robust enforcement will be critical for the administration's maximum pressure strategy to succeed, both immediately to drain the Iranian regime's resources for malign behavior and as a signal of America's commitment to maintaining the integrity of our sanctions architecture," they wrote. "The administration's maximum pressure campaign will not succeed if the Islamic Republic remains connected to SWIFT."

SWIFT is short for the Society for Worldwide Interbank Financial Telecommunication. It is based in Belgium, but its board includes executives from U.S. banks and federal law gives the administration authority to act against Iran's central bank and other banks covered by terrorism and money laundering sanctions.

President Donald Trump withdrew from 2015 nuclear accord in May and re-imposed some sanctions on Iran earlier this month over the objections of Iran and the other parties to the deal, including Britain, France and Germany. A second batch of sanctions will be re-imposed in November.

The letter was sent shortly after the European Union announced its first financial support package for Iran worth about $21 million to help keep the nuclear deal alive as numerous European companies withdraw from the country over fears of being subjected to U.S. sanctions.

It also came a day after Germany's foreign minister called for Europe to create a banking payments system independent of the United States, in another effort to maintain the agreement.

Heiko Maas' suggestion was part of a wider-ranging piece in the daily Handelsblatt on Germany's future strategy toward the U.S. He said he envisions Europe taking a "balanced share of responsibility" and being "a counterbalance when the U.S. crosses red lines."

"In this situation, it is of strategic significance that we say clearly to Washington: we want to work together, but we will not allow you to act over our heads to our detriment," Maas wrote. "That is why it was right to legally protect European companies from sanctions," he said. "That is why it is indispensable to strengthen European autonomy by setting up payment channels that are independent of the U.S., creating a European monetary fund and setting up an independent SWIFT system."