The United States' tightening grip on Venezuela’s oil exports could strangle the country's crude output and cut off President Nicolas Maduro's main economic lifeline, but it will have limited impact on the global market.

The US special forces veteran who spirited Nobel laureate María Corina Machado out of Venezuela has begged her not to return to the country, after a perilous rescue mission that lasted nearly 16 hours and was carried out largely in the middle of the night through rough waters.