The Trump administration is considering re-imposing a massive set of economic sanctions on Iran that were lifted by the Obama administration as part of the landmark nuclear agreement that gave Tehran billions in economic support, according to U.S. officials who told the Washington Free Beacon that Iran's military buildup and disregard for international law could prompt U.S. reprisal.

Secretary of State Rex Tillerson told Congress in a letter sent Tuesday that Iran is complying with requirements for its nuclear program imposed under the nuclear accord. However, Tillerson emphasized that Iran continues to be the world's leading state sponsor of terror.

Tehran's malign activities across the Middle East and elsewhere have prompted the Trump administration to place all aspects of the nuclear agreement under critical review, which is viewed by some as a first step to nixing some controversial aspects of the accord, including the massive sanctions relief package.

U.S. officials familiar with the review told the Free Beacon that Iran's continued support for terrorism has become a sticking point for the Trump administration as it reviews the agreement and the previous administration's policy toward Iran.

"I think the key is what comes next," one senior White House official familiar with the interagency review told the Free Beacon. "The question of ongoing sanctions relief will be critical—Iran has already gotten significant economic benefits from the nuclear deal and we need to take a hard look at what Iran is doing with the resources that continue to flow in."

The Trump administration has been paying close attention to Iran's ongoing military buildup, including its continued work on ballistic missiles and other offensive weapons aimed at interfering with U.S. operations in the Persian Gulf region.

"Yesterday was the annual Army Day celebration—also known as Death to Israel day—and they paraded some pretty serious new hardware through the streets," the White House official disclosed. "That has to be a significant concern."

The White House's national security apparatus will closely monitor Iran's behavior as it makes a decision about re-imposing sanctions lifted by the Obama administration.

Tillerson's emphasis on Iran's terror operation is "a first step, but we have to remain focused on the threat Tehran poses to America and our allies," the official said.

Obama administration officials, while selling the nuclear deal to Congress, vowed that Iran would roll back its nefarious activities if it received relief from sanctions.

Tillerson informed Congress this has not happened. After receiving billions in cash assets and other economic relief, Iran invested heavily in its military and the Iranian Revolutionary Guard Corps, or IRGC, which continues to meddle in Syria, Iraq, Yemen, and a host of other countries.

"Iran remains a leading state sponsor of terror through many platforms and methods," Tillerson told Congress. "President Donald J. Trump has directed a National Security Council-led interagency review of the Joint Comprehensive Plan of Action (JCPOA) that will evaluate whether suspension of sanctions related to Iran pursuant to the JCPOA is vital to the national security interests of the United States."

"When the interagency review is completed, the administration looks forward to working with Congress on this issue," Tillerson wrote.