US President Donald Trump has nominated a new head of US forces in Latin America, according to a statement, after an admiral stepped down from the role early.

Pentagon chief Pete Hegseth announced in the statement on Friday that Trump had appointed General Francis L Donovan to head the US Southern Command, a role that oversees the major US military buildup taking place in the Caribbean.

The appointment of Donovan, currently the vice commander of the Pentagon's Special Operations Command, would need to be confirmed by the Senate before he can take up the position.

The previous Southern Command head Admiral Alvin Holsey announced in mid-October that he would leave his position, and had reportedly expressed concerns about US strikes on alleged drug-trafficking boats.

Holsey officially stepped down from the role this month, only one year into his tenure, with neither he nor Hegseth having publicly provided a reason for his early departure.

The United States has amassed a huge flotilla of warships in the Caribbean as part of what Washington bills as counter-narcotics efforts and since September carried out strikes targeting alleged drug-smuggling vessels that have left more than 100 dead.

Trump's administration insists it is effectively at war with alleged drug traffickers, but experts say the strikes on the boats amount to extrajudicial killings even if they target known traffickers.

Venezuela's leader Nicolas Maduro has accused Washington of using drug trafficking as a pretext for regime change in Caracas.

Trump in an interview on Thursday with NBC News left open the possibility of war with Venezuela, and his top diplomat Marco Rubio vowed on Friday to enforce a blockade on the country's oil wealth. (AFP)