Caracas, September 7 (RHC)--  President Nicolas Maduro said Friday that he won't resume talks with the opposition until it rejects calls by a top supporter in Britain to give up Venezuela's sovereignty claims over the oil-rich contested territory of Essequibo.

The Venezuelan leader’s comments came after his chief prosecutor opened an investigation against Vanessa Neumann, the top envoy in London for opposition leader Juan Guaido.

“To return to the dialogue, we demand that they rectify their infamous purpose to surrender our territory. This decision represents the feelings of Venezuelans. It is a National Cause!," Maduro wrote on Twitter.

Government and opposition talks had been taking place under the sponsorship of Norway since April. But Maduro last month broke off the talks taking place on the Caribbean island of Barbados over the opposition's support for tougher U.S. sanctions to punish companies from third countries that do business in Venezuela.

On Thursday, Venezuelan Vice President Delcy Rodriguez released recordings in which Neumann can be heard urging a Guaido aide, Manuel Avendano, to give up the opposition's claim to the Essequibo region, disputed with Guyana.

In the recording, Neumann says that after speaking with the British Foreign Office, she recommends that the opposition "drop the topic" of Venezuela's claim to Essequibo in order to secure London's political support. Guyana is a member of the British Commonwealth.

Venezuelans have long claimed the mineral-rich region west of the Essequibo River in Guyana, arguing it was stolen from their country in the 19th century breakup of the former British colony.

In announcing charges Friday, Venezuela's chief prosecutor, Tarek William Saab, accused Neumann and Avendano of secretly negotiating a deal to drop Venezuela's claim to Essequibo in exchange for lucrative contracts with multinational corporations.