An Iranian newspaper report claimed Monday that the bomb used to assassinate a nuclear scientist last month was “made in the USA.”

The bomb used to kill Mostafa Ahmadi Roshan, 32, was one of two that were delivered to Iran via members of PJAK, the Party for Free Life of Kurdistan, a  Kurdish separatist group, the Resalat daily newspaper reported Monday.

The second bomb was discovered and defused by intelligence and security personnel deployed around Resalat Square in Tehran, according to the report.

Iran claimed last month it had arrested an unidentified number of unnamed suspects in connection with the assassination, saying the scientist’s killers had been “identified.”

The scientist, allegedly a chemical engineer, was killed on January 11 after a motorcyclist attached a magnetic bomb to his car. Iran claims that Roshan served as the deputy director of marketing at the Natanz nuclear facility. He was known as an oil industry expert at Sharif University of Technology, an institution linked with the Iranian Revolutionary Guards.

Enraged Iranian officials vowed retaliation against Israel, the U.S. and the UK over the assassination.

White House spokesman Tommy Vietor denied the United States had any involvement in the incident, saying the U.S. had “absolutely nothing to do” with the blast that killed Roshan. 

Several Iranian nuclear scientists have been killed and wounded in recent years.