Mohammad Sanusi Barkindo, secretary-general of the OPEC oil cartel, has died, Mele Kyari, the chief executive of Nigerian National Petroleum Corp, said on Wednesday.

Barkindo, who was 63 years old, was due to step down at the end of this month after six years as OPEC's secretary-general.

"We lost our esteemed Dr Muhammad Sanusi Barkindo," Kyari said on Twitter, adding that the death took place at about 11 p.m. on Tuesday.

"The death was a "great loss to his immediate family, the NNPC, our country Nigeria, the OPEC and the global energy community," he added.

Kyari said Barkindo died hours after meeting Nigerian President Muhammadu Buhari and giving the main speech at an energy summit in Abuja.

Barkindo said the oil and gas industry is "under siege" due to years of under-investment, adding that the resulting supply shortage could be eased if extra production from Iran and Venezuela was allowed to flow.