The Iranian Foreign Ministry summoned Azerbaijan’s ambassador on Sunday, accusing the country of colluding with the Israeli intelligence in the killing of an Iranian nuclear scientist last month, the state news agency IRNA reported.

The ministry handed a protest note to Azeri envoy Javanshir Akhundov and demanded the oil-rich former Soviet state prevent Israel’s Mossad spy agency from using its territory to carry out operations against Tehran, the report said.

Mostafa Ahmadi-Roshan, who worked at the Natanz uranium enrichment facility, was killed in a car bomb attack in Tehran on January 11.

Iran’s Supreme Leader Ayatollah Ali Khamenei blamed the killing on the United States and Israel.

The United States condemned the killing and denied any involvement. Israel has neither denied nor admitted blame.

Ahmadi-Roshan was the fourth scientist associated with Iran’s disputed nuclear program to have been assassinated since 2010.

Western powers suspect Iran of seeking to create a nuclear bomb and have tightened sanctions. Tehran says its program is aimed at the production of civilian energy.

Iranian President Ahmadinejad said on Saturday Tehran would make an important announcement on the progress of its nuclear program “in several days.”

The Foreign Ministry in Tehran also complained that Azerbaijan, which borders Iran and has friendly relations with the United States and Israel, mistreated Iranian officials and stopped Iranian trucks traveling through the country.

Ties between Tehran and Baku have deteriorated in recent years. Last month, Azerbaijan arrested two people allegedly linked to Iran’s intelligence services. Azeri authorities said the two men were plotting attacks against foreigners, including Israel’s envoy in Baku. Azeris are the largest ethnic minority in Iran.