British Prime Minister Theresa May greets Secretary of State Rex Tillerson in London on Thursday. May supports the Iran nuclear deal. (Pool photo/U.S. Embassy/Reuters)

The United States on Thursday waived sanctions on Iran in what was characterized as a holding action until the White House decides next month whether to continue with the landmark nuclear agreement by certifying Iran is meeting its commitments.

At the same time, the White House signaled its determination to confront Tehran over actions the United States considers in defiance of the intent of the 2015 deal.

“The administration seeks to bring a change in Iran’s behavior,” said a senior administration official who insisted on anonymity because he was not authorized to speak publicly on the matter. The official cited Iran’s ballistic-missile tests, support for terrorist groups such as Hezbollah and Islamic Jihad, backing of militias fighting in neighboring countries and human rights abuses, including the detention of several U.S. citizens.

Officials in the Obama administration who negotiated the nuclear agreement acknowledged that the other issues were problematic but said it was preferable to confront an Iran that is not armed with nuclear weapons.

By Oct. 15, President Trump must decide whether to certify Iran’s compliance with the deal, which was negotiated with the United States and five other world powers. Trump has said he is leaning toward not certifying it, which would give Congress the job of determining whether to reimpose sanctions and effectively walk away from the deal. The timing would place the debate in the middle of budget deliberations.

Eight times since the agreement took effect last year, the International Atomic Energy Agency has said Iran has fully upheld its end. But administration officials repeatedly have accused Iran of violating the deal’s “spirit” and undermining the goal of peace.

“You’ll see what I’m going to be doing very shortly in October,” said Trump on Thursday. He has been increasingly irritated at having to renew parts of a deal he had vowed to dismantle.

“We are not going to stand what they are doing with our country,” Trump said. “They’ve violated so many different elements, and they’ve also violated the spirit of that deal.”

In London, Secretary of State Rex Tillerson said on Thursday that the deal had failed to stop Iran from being a destabilizing factor in the region.

“In our view, Iran is clearly in default of the expectations,” Tillerson said.

While the agreement known as the Joint Comprehensive Plan of Action was narrowly defined as one that limited Iran’s nuclear program, administration officials frequently point to an aspirational sentence in the preface to make the case Iran is not living up to its commitments. It says the participants “anticipate that full implementation of this JCPOA will positively contribute to regional and international peace and security.”

Nikki Haley, the U.S. ambassador to the United Nations, laid out the case for decertification earlier this month, saying the agreement does not serve U.S. national interests.

When the U.N. General Assembly meets next week, U.S. officials are expected to discuss the deal with negotiating partner countries — Britain, France, Germany, China and Russia. Some U.S. officials hope for support to modify the agreement. But France has ruled it out, Iran has said it has no interest in reopening talks and British Prime Minister Theresa May told Tillerson that the deal prevents Iran from obtaining nuclear weapons.

Opponents of the deal are telling Trump that extreme measures may be needed. A memo obtained by Foreign Policy urges Trump to declare that Tehran is not complying with the agreement, and threaten a “de-facto global economic embargo” on Iran if it does not satisfy U.S. demands. According to the magazine, the embargo would reimpose sanctions lifted under the deal and add more.

Foreshadowing more sanctions, the Treasury Department on Thursday imposed financial sanctions on companies and people who mostly had ties to the Islamic Revolutionary Guard Corps, a hard-line branch of the armed forces that has opposed the nuclear deal and aspires to keep Iran free of Western influences.

The new sanctions cover companies that provided cranes and airline services to Revolutionary Guard units and two private Iranian computer security companies that allegedly attacked U.S. banks and stock exchanges in 2011 and 2012.

Sen. Bob Corker (R-Tenn.), chairman of the Foreign Relations Committee, said he is preparing for a change in U.S. policy.

“We’re working hand in hand with the White House and with the State Department to be prepared, to be prepared to deal with this issue depending on the outcome,” he said.

Karoun Demirjian contributed to this report.