A top Iranian nuclear scientist has been killed by a car bomb in Tehran amid escalating conflict between the West and Iran over the Middle Eastern country’s nuclear development.

The explosion killed Iranian nuclear scientist Mostafa Ahmadi Roshan and his colleague and seriously injured another person.

Roshan, a professor at the University of Tehran, was a director of Iran’s key uranium enrichment facility in the central region of Natanz.

Iran accused Israel and the U.S. of assassinating Roshan to halt its nuclear program.

But both Israel and the U.S. have denied their involvement in the blast. The two nations were also accused of masterminding a fatal computer virus attack on Iran’s uranium enrichment facility in 2010.