However, a British deputy commander in the global coalition against the Islamic State group contradicted the risk of an attack.
"There's been no increased threat from Iranian backed forces in Iraq and Syria," Maj. Gen. Chris Ghika told reporters Wednesday. "We're aware of their presence, clearly, and we monitor them, along with a whole range of others because that's the environment we're in."
Ghika said the anti-ISIS task force had no intention to change protection measures or its escalation processes despite the developments in the Persian Gulf this week.
"There are a substantial number of militia groups in Iraq and Syria and we don't see any increased threat from many of them at this stage," he said.
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NBC News asked the British Ministry of Defense on Thursday whether it would raise the threat level for U.K. forces and diplomats in Iraq. A spokesperson would not be drawn on that question but said the ministry "has long been clear about our concerns over Iran’s destabilizing behavior in the region” and that the security of personnel and assets is under constant review.
However, Britain's Foreign Secretary Jeremy Hunt later tweeted that his country's policy is in line with the U.S. after having spoken with Secretary of State Mike Pompeo earlier in the week in Brussels. "We share the same assessment of the heightened threat posed by Iran. As always we work closely with the [U.S.]," he said.
Germany's Foreign Minister Heiko Maas said Wednesday that he made it clear to Pompeo in a meeting earlier this week that a unilateral strategy of increasing pressure against Iran was ill-advised.
"Maximum pressure always carries the risk of an unintended escalation," Maas said. "If you take a look at what other hot spots and sources of conflict are there in this region, then we certainly do not need one thing at the moment: an additional fuse."
The dispute over the risks is a reflection of the diverging tactics of the U.S. and Europe to maintain productive relations with Iran, said Sanam Vakil, senior research fellow for the Middle East North Africa program at the London think tank Chatham House.
While Europe opts for a more cautious approach in engaging the Iranian regime, in part due to its close proximity to the Middle East, the U.S. has adopted a strategy of "fear-mongering and posturing," she said.
"[Europeans] ultimately believe the Trump administration has manufactured a crisis and this crisis has prevented them from addressing the other equally important issues that impact European security," she said.
The current situation stems from the U.S. withdrawal from the Iran nuclear deal, she said, adding that the deal was working and Iran was in compliance.
Europe and other allies could attempt to kickstart diplomacy with Iran to protect the nuclear deal, known as the JCPOA, Vakil said, but it would require a very public and meaningful effort with no guarantee the U.S. wouldn't obstruct the process.
Senior State Department officials told NBC News on Wednesday that intelligence on threats to peace and security have been shared with British, French and German allies, who were also asked to use their influence with the Iranian regime to de-escalate the situation.
“I would say it would be an act of gross negligence if we did not take the necessary precautions in the light of credible threat streams,” one official said. "That does not mean we are rushing to a conflict."
Ahmed al-Sahaf, spokesman to Iraq's Foreign Affairs Ministry, told NBC News that the situation in Iraq remains stable. The government "is cooperating with all countries that are part of the latest development in the region to reach a balanced solution," he said.
Linda Givetash is a London-based producer for NBC News.
Abigail Williams is a producer and reporter for NBC News covering the State Department.