Iranian scientists have produced their first nuclear fuel rod, Iran’s nuclear agency said Sunday, another step despite United Nations sanctions and measures by the United States and others to stop the nation’s atomic work and shut down any possible pathways to weapons production.

Iran has long said it is forced to seek a way to manufacture the fuel rods on its own, since the sanctions ban it from buying them on foreign markets. Nuclear fuel rods are tubes containing pellets of enriched uranium that provide fuel for reactors.