Venezuelan President Nicolas Maduro has signed an agreement with Turkey to extract gold in his country's south where large areas have been devastated by illegal mines.

"Turkey's investment is intended to continue developing gold (in) the Mining Arc (of Orinoco)," Maduro said, referring to a region rich in gold, iron, coltan and other minerals, which have been subject to illicit extraction.

"We are going to develop these gold fields, and I wish you the best of luck so that what we are signing... becomes an example of ecological development that is respectful of nature and very productive," the leftist leader said at Friday's signing.

Activists have long denounced "ecocide" in the South American nation's southern region.

Authorities say illegal miners fell and burn trees, contaminate rivers and engage in underground drilling that harms the environment as well as Indigenous communities.

On Friday, Maduro also signed agreements with Turkey related to the construction of an ammonia refinery and the tapping of gas reserves.

"They are three great projects of the future for petrochemicals, gas and gold," said Maduro, who is campaigning ahead of the July 28 presidential election.

Turkish President Recep Tayyip Erdogan is scheduled to visit Venezuela this year, but no date has been announced.

Erdogan visited the country in December 2018 to lend support to Maduro after the United States and several European nations disavowed the Venezuelan leader's re-election over accusations of fraud.