Veolia last month offered to pay energy group Engie 2.9 billion euros (2.65 billion pounds) for a 29.9% stake in Suez, with a view to subsequently taking full control of its rival by buying up more shares, a move Suez views as hostile.

Veolia's offer remains valid until Sept. 30.

"There have been multiple conversations ... The goal remains to find a middle ground and to end the conflict, the source told Reuters.

The French state holds a 23.6% stake in Engie and has tried to ease tensions. Engie, which owns almost 32% of Suez, rejected Veolia's initial advance but has said it would consider a higher offer.

(Reporting by Benjamin Mallet; Writing by Matthias Blamont; Editing by Andrew Heavens)