I would be very surprised if they are not already assembled into warheads.
The only thing holding them off is that they will probably want to have enough to actually make a huge impact, and pre-position their attacking entities for the deployments in the West.
When all their ducks are in a row...then they pull the trigger.
This came across the wires this morning. Low levels of Iodine 131 were found in the Czech Republic and other areas of Europe. Iodine 131 is a product of plutonium fission and the report says it the iodine 131 is not from Fukushima.