ESSEN, Germany Efforts to sell uranium enrichment company Urenco, in which E.ON (EONGn.DE) holds a 16.7 percent stake, have not failed, E.ON's Chief Executive Johannes Teyssen said, but warned the process remained challenging due to the asset's complex ownership.

"The sale has not failed. Of course, talks are challenging," Johannes Teyssen told shareholders at the group's annual general meeting on Wednesday, pointing to the involvement of several owners, including RWE (RWEG.DE), which also holds 16.7 percent.

With a total value seen at about 10 billion euros ($10.9 billion), even a sale of a stake in Urenco -- in which the British and Dutch governments also hold a third each -- could be lucrative. Talks to divest the asset have been going on for at least half a decade.

(Reporting by Christoph Steitz; Editing by Maria Sheahan)