The US appears confident that its extra military presence in the Gulf is affecting Iran’s activities in the region, but insists that the goal is still to bring Tehran to the negotiating table.
Speaking at a breakfast hosted by news website Al-Monitor in Washington on Tuesday, Kathryn Wheelbarger, a senior defence policy official, described the threat from Iran as "akin to a campaign against us".
Ms Wheelbarger said officials were called in to assess Iran's threat to maritime security after last month’s attack on tankers off the UAE, because there were concerns for the safety of forces in the region.
US National Security Adviser John Bolton has accused Iran’s Revolutionary Guard of being behind the tanker attacks.
And a report that summarised the preliminary findings of an investigation by the UAE, Norway and Saudi Arabia concluded that a "state actor" was most likely behind the operation.
Last month, the US moved the aircraft carrier USS Abraham Lincoln and B-52 bombers to the Gulf. It has also announced plans to send 1,500 more troops to the region.
Ms Wheelbarger described the continued threat from Iran as “credible, intentional and co-ordinated”, but said that US presence in the region was tempering Tehran's actions.
The US intends to continue its presence or to send extra force to stop the situation worsening and maintain regional balance, she said.
Ms Wheelbarger said she would be "reluctant to say that any one decision resulted in this”, referring to the recent US designation of the Guard as a foreign terrorist organisation,
The US has previously said it will respond with military force if it or its interests are attacked by Tehran.
Ms Wheelbarger also singled out Russia and China as competitors to America’s interests in the region.
She said plans by Turkey to acquire an S-400 Russian defence missile system, despite the US threatening sanctions against Ankara, is “an absolute no-go” for the country. She called Russia an “unreliable partner”.
“This isn’t just one transaction. This is about continued alignment and inter-operability with Nato,” Ms Wheelbarger said.
With less than a month before the S-400 deal is complete, she said she still believed there was a chance that Turkey would not take the Russian system.
She said relations between Ankara and Moscow were being tested by the situation in Idlib, the last rebel-held area of Syria.
“Turkey is learning the hard way that Russia can’t be relied on,” Ms Wheelbarger said, referring to the Russian offensive in Idlib.
A de-escalation zone was agreed to by the two countries, but Russia has carried out heavy bombing in the area in recent weeks.
Ms Wheelbarger said the US was a strategic ally of Turkey and would ease Ankara's concerns and protect its economy if they were to pull out of the missile deal.
On Friday, the US government ordered the termination of Ankara’s participation in its F-35 programme by the end of July if it did not back down on the deal.
It has also suspended training of Turkish pilots in the F-35 fighter jets.