A consignment of enriched uranium - enough to make a nuclear weapon, according to a U.S. expert - rumbled out of a Ukrainian railway depot late on Saturday, March 24 bound for Russia, a move designed to coincide with an international summit on nuclear security, Reuters reported.

The 19 kilograms (42 pounds) of spent highly enriched uranium, loaded in four containers onto rail carriers in a high-security operation, was the last such material to be removed from the ex-Soviet republic under a two-year programme with the United States and Russia.

The completion of the programme was timed to raise the curtain on a March 26-27 nuclear security summit in Seoul, South Korea, to be attended by leaders from 50 countries including U.S. President Barack Obama and Ukraine's Viktor Yanukovich.

The summit will focus on measures to protect nuclear materials and facilities and to prevent illicit trafficking.

Altogether 200 kilograms of weapons-grade material have been removed from Ukraine and sent back to Russia - the originating country - since May 2010.

The material will be delivered to the Mayak reprocessing nuclear facility in Russia's Ural mountains - a rail journey of about five days from Kiev.

The enriched uranium shipped out on Saturday had been used in a reactor at a nuclear research facility in Kiev.