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(CNN) —  

Iran is set to announce Wednesday that it will reduce its commitments to the international nuclear pact it signed in 2015 as the US moves a Navy strike group and B-52 bombers to the region to counter perceived threats from Tehran and Secretary of State Mike Pompeo made a surprise visit to the region.

Exactly a year to the day after President Donald Trump announced the US was abandoning the landmark agreement meant to curb Iran’s nuclear program, President Hassan Rouhani will relay the decision to the European Union in a letter, while the British, French, German, Russian and Chinese ambassadors will be told in person at the foreign ministry, according to Iran’s state media IRNA.

“Iran exercised restraint over the past year, but the other parties to the deal failed to adhere to their commitments so that Iran had no other way but to reduce its commitments under the deal,” the letter is expected to read, according to IRNA.

’Iranians were going to react’

Iran’s decision to ease its adherence to the nuclear deal isn’t expected to unravel the pact anytime soon, according to analysts who said that the remaining parties will likely remain committed to shoring up to agreement.

But it could further strain ties between the US and its European allies and heighten global tensions as Washington moves military firepower into the region and Iran prepares to adjust its approach to the deal. While it remains to be seen how that plays out, the one thing that was certain, said Henry Rome, an analyst at the Eurasia Group, was that after a year of US pressure, Iran was going to respond.

“The other shoe that was always going to drop is that the Iranians were going to react,” Rome said. While Tehran has a range of actions it can take as it tweaks its adherence to the deal, Rome and others said they expect Iran to carefully calibrate its course. “There are extremely provocative actions they could take, but we think they’ll choose something moderate,” Rome said.

Mark Dubowitz, CEO of Foundation for Defense of Democracies, and an advocate for tough measures against Tehran, said, “The regime in Iran remains committed to nuclear weapons capability.”

“Any Iranian move to expand their nuclear program should be met with the most severe sanctions – and an unambiguous warning from Washington that all other instruments of American power are available to stop the ayatollahs’ atomic drive,” he said.

Iran’s announcement is expected as the US moves a carrier strike group and B-52 bombers to the Strait of Hormuz after the Pentagon said “specific and credible” intelligence suggested Iranian forces were targeting US troops in Syria, Iraq and at sea.

Surprise visit

On Tuesday, the Pentagon offered further detail, telling CNN that intelligence suggested Iranian forces were moving short- and medium-range ballistic missiles aboard boats in the Persian Gulf.

The Defense Department is now considering sending additional firepower to the region, including anti-missile defense systems, according to several US officials with knowledge of the situation.

As the strike group steamed toward the Middle East, Pompeo canceled an expected visit to Berlin to meet with Chancellor Angela Merkel to make an unannounced stop in Baghdad.

The top US diplomat met with Iraq’s prime minister, president and other officials in a roughly four-hour visit, according to pool reports from journalists traveling with him.

Speaking to reporters, Pompeo said he discussed the “threat stream we had seen” from Iran and stressed “the importance of Iraq ensuring that it’s able to adequately protect Americans in their country.”

“We don’t want anyone interfering in their country, certainly not by attacking another nation inside of Iraq and there was complete agreement,” he said.

Pompeo hinted that the future of US-Iraq relations depends in part on the way Baghdad approaches Tehran. “We want to make sure that Iraq is positioned so that the relationship that we’ve built with them and that our allies in the region have built with them – allies that range all across the Gulf, who understand that the primary threat in the Middle East is Iran – remains strong and those relationships remain strong,” he said.

Pompeo has now left Iraq to fly to London and pick up his previously planned itinerary.

Maximum pressure

Iran’s decision to tweak its adherence to the deal comes after a year in which the Trump administration has worked to limit any benefits Tehran might gain from the deal through an increasingly intense “maximum pressure” campaign.

Pompeo described that initiative and its aims in a May 21 speech that laid out 12 ways the US wants to see Iran change and start being a “normal” country – a speech that many saw as a call for regime change in everything but name.

Since then, the US has reintroduced all nuclear-related sanctions among a slew of other punitive measures. In the past month, it has moved to cut off Iran’s oil revenues, its chief source of foreign income, put curbs on its civilian nuclear work, and designated Iran’s Revolutionary Guard Corps, the elite military group with deep political and economic influence, as a terrorist entity.

Iran will inform European Union Foreign Policy Chief Federica Mogherini – who coordinates the Joint Commission that supervises the monitoring of the implementation of the Iran deal – of the legal and technical details of the changes in a letter written by Iran’s Foreign Minister Mohammad Javad Zarif.

“The text of the letters will be among the confidential documents of JCPOA Joint Commission, but the news about them will be published,” IRNA wrote, adding that Tehran’s specific request is “to return to banking and oil trade conditions before US exit from the deal on May 8, 2018.”

The European Union and other parties that remain in the agreement declined to comment, but pointed to a strongly worded May 4 statement after the US decision not to extend waivers for Iranian oil trade or fully renew waivers for nuclear non-proliferation work with Iran.

The statement noted Tehran’s compliance with the deal so far and the group’s strong belief that the pact contributes to stability in the Middle East. It also expressed “deep regret” – diplomatic speak for anger and frustration – about the US decision to reimpose sanctions lifted after the deal, formally known as the Joint Comprehensive Plan of Action.

The steps Iran takes now will be as much directed at Europe and other parties to the deal as it is to the US and its regional allies.

“They have a lot of audiences that care about their decision here,” said Rome. “With Washington they want to push back, they’re pushing Europe to provide more political and financial support, with domestic audiences they want to show that they’re serious about defending Iranian interests.”

But as Tehran calibrates its response, it will have to take care not to “spook the Chinese and the Russians or take such a dramatic step that it sparks a US or Israeli military attack or causes Europe to turn their backs,” Rome said.

Levels of response

At the most extreme end of the spectrum, Iran could exceed the limits on its stockpile of low-enriched uranium, the size of which determines how close they are to a weapon. The US has just revoked waivers that allowed Iran to export those excess stockpiles. “Iran could say we are only doing this because Trump has forced us to,” Rome said.

Iran could take steps to reduce its low-enriched uranium production, he said, “but if they keep doing everything they’re doing it would absolutely violate the agreement. That’s the choice the administration wanted to force on the Iranians by revoking those waivers.”

Tehran could also start testing larger numbers of centrifuges or deny international inspectors access to its nuclear sites. On the lower end of the scale, it could start exceeding its allowed accumulation of heavy water.

“What the Iranians are pushing at here is seeing how they can take this idea of incremental violation before it hits a redline,” Rome said. “They’re very experienced at using nuclear advancements to signal different things to different parties without triggering a nuclear crisis. I think they’ll find they have a long way to go.”

CNN’s Barbara Starr, Jenny Hansler, Steve George and Donna Borak and contributed to this report.