The international body charged with conducting inspections of Iran's nuclear facilities on Monday said Tehran is complying with its initial commitments under the deal it struck with the U.S. and five other world powers last fall.

The International Atomic Energy Agency submitted a report Monday on Iran's compliance under the agreement which is aimed at freezing and rolling back parts of Tehran's nuclear program in exchange for sanctions relief. Monday was the start date for the six-month preliminary agreement.

The U.S. and the European Union agreed with the IAEA's report and will begin providing limited sanctions relief as scheduled. Iran will receive a total of $4.2 billion in direct sanctions relief over the course of the six-month agreement if it continues to fulfill its commitments.

“Iran has begun to take concrete and verifiable steps to halt its nuclear program,” State Department spokeswoman Jen Psaki said in a statement. “These actions today are significant steps in our efforts to achieve a diplomatic solution to prevent Iran from obtaining a nuclear weapon.

“The coming negotiation to reach a comprehensive agreement that addresses all of the international community’s concerns will be even more complex, and we go into it clear-eyed about the difficulties ahead,” she said.

Psaki said the talks offered an “unprecedented opportunity to see if we can resolve this most pressing national security concern peacefully.”

A senior administration official said the IAEA verified that Iran has stopped enriching uranium above 5 percent and has begun the process of diluting half of its 20-percent enriched uranium stockpile to 5 percent and turning the other half into material that cannot be used for the creation of a weapon.

“This increases our confidence that Iran cannot break out with a nuclear weapon without the rest of the world knowing in advance,” the official told reporters on a conference call Monday, noting that the IAEA will roughly double the size of its inspection team.

The partial sanctions relief, the official stressed, is only a fraction of what Iran needs to help its struggling economy get back on track, and if there are any violations, the U.S. is committed to reinstating the sanctions.

“This does not in any way mean Iran is open for business,” the official said.

Der Spiegel in early January reported that international investors are flocking to Tehran to re-enter Iran's market as the sanctions are lifted. The paper quoted the head of the German-Iranian Chamber of Industry and Commerce in Tehran, characterizing the business opportunities opening up as a “chance of a century.”

The sanctions relief allows Iran to continue its crude oil exports to six current customers but only at previously established reduced levels. It also lifts sanctions over the next six months on non-U.S. firms engaging in transactions related to Iran's petrochemical exports, certain trade in gold and precious metals with Iran and the provision of goods and services to Iran's automotive sector.

In addition, the Obama administration is working with its international partners and Iran to establish financial channels to enable Tehran to make payments for humanitarian transactions and medical expenses, university payments for Iranian students studying abroad and the payment of Iran's United Nations dues and obligations.

The sanctions relief comes the same day U.S. officials expressed alarm over the United Nations’ decision to allow Iran to join Syrian peace talks in Geneva this week aimed at setting up a transitional government.

Over the weekend, Ban Ki-moon, the United Nations secretary general, invited Iran to join the peace conference but the U.S. is arguing that the invitation must be rescinded because Tehran disagrees with the need to set up a transitional government, a condition for attendance.

Reacting to the news, the Syrian opposition is threatening not to show up in Switzerland on Wednesday, when the talks are set to begin.

Obama administration officials have said negotiations with Iran on the nuclear agreement are separate from any other issue, including Tehran's backing of the Assad regime in Syria's civil war or its state-sponsorship of terrorism around the world.

“We continue to have major concerns about various aspects of Iranian policy… and we will continue to confront them on that,” an official said. “But these are separate tracks.”

This story was published at 11:51 a.m. and has been updated.