The United States has given weapons-grade uranium to 43 countries, including Pakistan, since the 1950s under the Atoms for Peace programme and is making little effort to get them back, a US government department reported.
The Department of Energy said in a report that among the countries, which have refused to return the material are Pakistan, Iran, Israel, Mexico, Jamaica and South Africa.
The reasons for declining vary. Some of the bomb-grade uranium is in use at research universities and institutions that do not want to give it up.
Jon Wolfsthal, who ran the recovery programme from 1995 to 1997, said one important reason why so little uranium has been returned is that 'we are charging these countries $5,000 kilogramme to get it back'.
The fee structure was set up in 1996, to help pay for the programme.
