Royal Dutch Shell has sold some of four oil fields up for grabs in Nigeria, it said on Wednesday, as the oil and gas company pushes ahead with global asset sales to cut costs.

Shell last year put up for sale its 30 percent shares in four oil blocks in the Niger Delta -- Oil Mining Licence (OML) 18, 24, 25, 29 -- as well as a key pipeline, the Nembe Creek Trunk Line.

"We have signed sales & purchase agreements for some of the Oil Mining Leases, but not all that we are seeking to divest," a Shell spokesman said.

No details were available on the value of the deals signed, nor when the full process will be completed.

France's Total and Italy's Eni are also set to raise revenue from the sale of their 10 percent and 5 percent shares in the assets. The Nigerian National Petroleum Corporation (NNPC) owns the remaining 55 percent.

The Financial Times on Wednesday reported that Shell is close to selling the assets for about $5 billion to domestic buyers.

In March, Reuters reported that Nigerian firms Taleveras and Aiteo made the highest bid of $2.85 billion for the biggest of the four oil fields, OML 29.

Shell, along with many other oil majors, is undergoing a broad process of asset sales across the world in an effort to cut costs and boost profits.

Other companies, including Total, Eni, Chevron and ConocoPhillips have sought to pull out of the oil-rich West African country which has been plagued by oil theft.

Reporting by Ron Bousso