President Donald Trump has confirmed reports he authorised the CIA to conduct covert operations inside Venezuela - and said he was considering strikes targeting drug cartels there.

US forces have already conducted at least five strikes on suspected drug-carrying boats in the Caribbean in recent weeks, killing 27 people. UN-appointed human rights experts have described the raids as 'extrajudicial executions'.

Speaking in the Oval Office, Trump said the US 'is looking at land' as it considers further strikes in the region.

Trump has sought to increase pressure on President Nicolas Maduro, who the US and others do not recognise as Venezuela's rightful leader following disputed elections.

The increased US military presence in the region has raised fears in Caracas of a possible attack.

According to the New York Times, Trump's authorisation would allow the CIA to carry out operations in Venezuela unilaterally or as part of any wider US military activity.

It remains unknown whether the CIA is planning operations in Venezuela, or whether those plans are being kept as contingencies.

Trump stated, 'I authorised for two reasons really... Number one, they [Venezuela] have emptied their prisons into the United States of America. And the other thing are drugs.'

While Maduro's government has not commented on the CIA authorisation directly, Vice-President Delcy Rodriguez struck a defiant tone on television, warning against aggressors.

In the most recent US strike on Tuesday, six people were killed when a boat was targeted near Venezuela's coast.

The strikes form part of a larger military effort to pressure Maduro's government, which includes the positioning of significant air and naval assets in the region.

Maduro has repeatedly denied allegations of his involvement in drug trafficking and condemned the strikes.