US President Donald Trump has acknowledged that he has authorised the CIA to conduct covert operations in Venezuela - a highly unusual admission of what is normally a highly sensitive and tightly guarded state secret.

The authorisation - more typically known as a presidential finding - could give the agency broad leeway to conduct operations in the region, including lethal strikes against suspected drug traffickers or broader operations aimed at destablising or toppling the regime of Nicolas Maduro.

Previous presidential findings have ultimately led to drone strikes on militants overseas, money and weapons funnelled to insurgencies, and even efforts at full regime change.

Most, however, remain classified.

According to US law, presidents may authorise covert actions if they determine that these operations are "necessary to support identifiable foreign policy objectives...[and] important to the national security of the United States."