Iran has intensified efforts to seal off its near bomb-grade uranium cache by collapsing tunnels and planting explosive mines, according to sources familiar with US intelligence cited by CNN.

Access to roughly half a ton of highly enriched uranium has become far more difficult, dangerous and time-consuming than a month ago when President Donald Trump signaled possible military seizure.

The fortifications complicate Trump administration negotiations with Tehran over removing and destroying the stockpile, amid conflicting accounts and unclear terms of a draft deal.

Officials say any extraction would require excavation, de-mining operations, and specialized nuclear handling equipment.

Read more at CNN.