ABUJA - Nigeria's President Muhammadu Buhari expressed concern on Friday over large-scale crude oil theft, saying it was affecting the country's revenues "enormously".

Nigeria lost $1 billion in revenue during the first quarter of this year due to crude theft, the oil regulator has said.

Nigeria is unable to meet some of its financial obligations to its citizens due to the oil theft, Buhari told government workers who are requesting a pay increase to help deal with double-digit inflation.

"On your request for a salary review, I wish to urge you to appreciate the revenue constraints being presently faced by government which is caused mainly by the activities of unscrupulous citizens through the theft of our crude oil, a major contributor to our revenue base," Buhari said.

Crude theft poses an existential threat to Nigeria's oil industry, the local head of Shell has said, resulting in the shutdown of two of its major pipelines.

Nigeria is currently battling to stabilise its ailing currency, to curb surging inflation and boost growth after the economic disruption caused by the COVID-19 pandemic.

Annual inflation in Nigeria hit a 17-year high in July, data showed on Monday.

Buhari also blamed the war in Ukraine for the rise in global food prices and high transportation costs for goods and services.

He instructed security agencies to speedily clamp down on those involved in oil theft in the Niger Delta, adding that Nigeria was also strengthening cooperation with its neighbours to stop criminals syphoning away stolen crude by sea.

"We will not allow a few criminals to have unfettered access to the nation's oil supply," Buhari said.

(Reporting by Felix Onuah Editing by Gareth Jones Writing by Chijioke Ohuocha; Editing by Susan Fenton and Gareth Jones)