UN nuclear inspectors began a critical mission to Iran on Sunday to probe allegations of a secret atomic weapons program amid escalating Western economic pressures and warnings about safeguarding Gulf oil shipments from possible Iranian blockades.

The inspectors received a frigid welcome as they were greeted by a dozen Iranian hard-liners carrying photos of slain nuclear expert Mostafa Ahmadi Roshan at Tehran’s Imam Khomeini airport early Sunday.

Iranian state media allege that Roshan, a chemistry expert and director of the Natanz uranium enrichment facility in central Iran, was interviewed by IAEA inspectors before being killed earlier this month in a targeted bomb attack that Iran claims is part of an Israeli-led covert campaign of sabotage and slayings.

Roshan was at least the fourth member of Iran’s scientific community to be killed in apparent assassinations.

In Vienna, the IAEA said it does not know Roshan and has never talked to him.

Iran also has accused the IAEA in the past of security leaks that expose its scientists and their families to the threat of assassination by the US and Israel.

The ISNA news agency reported Sunday that the Islamic Republic said it would cooperate with the IAEA team but indicated it would not give up uranium enrichment, which it considered a sovereign right.

“We have always been open with regards to our nuclear issues, and the IAEA team coming to Iran can make the necessary inspections,” Ali-Akbar Velayati, advisor to Supreme Leader Ayatollah Sayyed Ali Khamenei, told the ISNA news agency.

“We will, however, not withdraw from our nuclear rights as we have constantly acted within international regulations and in line with the laws of the non-proliferation treaty,” Velayati said.

Meanwhile, Iran’s parliamentary speaker, Ali Larijani, called the visit a “test” for the UN agency, according to the website of the official IRIB state broadcaster.

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