Iran’s foreign minister on Wednesday accused the United States of being involved in the disappearance of an Iranian scientist with alleged links to Iran’s nuclear program.

The charge comes less than a week after Iran reached tentative accords with the United States and other major powers on addressing questions about its nuclear ambitions, including letting international inspectors visit its newly disclosed uranium-enrichment site near Qom. The charge also comes as the United States has raised questions about Americans being held in Iran.

The scientist, Shahram Amiri, vanished during a pilgrimage to Saudi Arabia four months ago; Iran previously called on Saudi Arabia to help locate him. He is a researcher at Malek Ashtar University, which is connected to Iran’s Revolutionary Guard Corps and was listed by the European Union last year as an entity linked to Iran’s nuclear activities or weapon delivery systems.