US Secretary of State Mike Pompeo criticised Tehran on Thursday, calling to reject its "nuclear extortion".
"Iran's expansion of proliferation-sensitive activities raises concerns that Iran is positioning itself to have the option of a rapid nuclear breakout", he said.
Tehran cancelled the accreditation of a UN nuclear inspector earlier in the day. According to the Iranian authorities, the female official triggered an alarm at the entrance to the Natanz uranium enrichment plant last week and as a result, was barred from inspecting the facility.
The organisation stated that she could have been carrying a "suspect product" on her, but it is unclear if anything prohibited was found in her possession. The incident was reported to the International Atomic Energy Agency, while the inspector left Iran for Vienna.
At the same time, US envoy to the IAEA Jackie Wolcott stated that Iran's move was "an outrageous provocation", noting that it was an "unwarranted act of intimidation".
Raising Tensions Over Nuclear Programme
The incident occurred amid another decision by the Islamic Republic to suspend part of its obligations under the Joint Comprehensive Plan of Action, also known as the Iran nuclear deal. Tehran has begun to use centrifuges at the Fordow nuclear site, vowing to increase its stockpile of enriched uranium (now around 500kg) by some 6kg per day.
This is the fourth such step by Iran since 8 May, the first anniversary of the United States' unilateral withdrawal from the nuclear accord, when the country announced a gradual reduction of its JCPOA obligations.
Tehran later stressed that it would start abandoning some parts of its nuclear obligations every 60 days unless the accord's European signatories ensure Iran's interests amid Washington's reinstated sanctions, urging them to save the deal.
In the meantime, Washington is continuing to slap sanctions on the Islamic Republic, while US-Iran relations are also deteriorating due to the tensions in the Middle East.