Iran has continued buying parts for its nuclear program using covert means despite mostly keeping to an interim deal with six world powers, a senior US official said Sunday.

Vann Van Diepen, who oversees non-proliferation issues for the State Department, told Reuters that while the parts are not expressly forbidden by the nuclear deal, a UN embargo on selling nuclear military or nuclear materials to Iran remains in place.

“They still continue very actively trying to procure items for their nuclear program and missile program,” said Van Diepen, the principal deputy assistant secretary of state for international security and non-proliferation.

“We continue to see them very actively setting up and operating through front companies, falsifying documentation, engaging in multiple levels of trans-shipment … to put more apparent distance between where the item originally came from and where it is ultimately going.”

Under a six-month interim deal, which officially took effect January 20, Iran agreed to freeze its uranium enrichment program in return for sanctions relief worth some $6-7 billion, including the transfer of some $4.2 billion in frozen overseas funds.

Talks on a final deal got underway in Vienna last month, and the next round is scheduled to take place Tuesday and Wednesday. The sides have set a soft deadline to reach an agreement by July, but it can be extended by another half year if both sides agree.

Van Diepen couldn’t confirm what components Iran has been importing, but a 2006 UN embargo prohibits all charter nations from providing Iran with any materials related to its nuclear or missile development programs.

The illicit activity would lend some credibility to those who argue that the sanctions relief has opened the door for Iran to do more illicit business.

The West suspects Iran’s nuclear program has a military dimension. Tehran denies the charge saying its nuclear program has aimed at peaceful purposes like power generation and medical treatment.

Iran has kept to its commitments concerning uranium enrichment, Reuters reported, citing unnamed diplomats, but procuring missile components and other materials that could be related to its nuclear program were not prohibited as part of the agreement. In fact, 200 Iranian lawmakers said in a recent statement that the country’s negotiators should not accept any discussion of the military and missile programs, which Tehran says have no connection to its nuclear program.

Van Diepen said he has not seen much, if any change in Iran’s actions over the past six months as it relates to obtaining components for its war machine.

However that could be because Iran does not see a permanent deal in the near future. Iranian Foreign Minister Mohammad Javad Zarif said as much when discussing the upcoming round of talks.

“We don’t expect to reach a deal in this round of talks. Nor was a deal on the agenda for this round of talks. We have agreed to discuss a number of issues in this round,” he said.

According to Van Diepen, though, progress in the talks could make a difference.

“Obviously if the negotiations succeed then there should therefore be a corresponding decrease in Iranian proliferation activity,” he said.

The Associated Press contributed to this report.