NEW YORK -- A group led by U.S. private-equity firm Blackstone Group is close to acquiring French water-and-energy conglomerate Suez SA's water- treatment-supplies unit for roughly $4 billion, people familiar with the situation told The Wall Street Journal.

The deal still requires approval by Suez's board and could fall apart at the eleventh hour, say these people, though both sides are aiming to unveil an agreement this week.

If Blackstone is successful in sealing the deal, it would be the latest sign of the increasing role that private-equity firms have been playing in this year's merger scene. On both sides of the Atlantic, as strategic buyers have been sidelined to tend to corporate scandals or ailing businesses, private- equity buyers, flush with cash, have been making big, splashy purchases.

In February, Blackstone, acting solo, bought TRW Automotive from its parent, TRW Inc., for $4.7 billion. A few months later a consortium of private-equity firms won a hotly contested auction to buy the telephone-directories unit of Italy's Seat Pagine Gialle SpA in two transactions, valued at about $6 billion. The total represented Europe's biggest-ever private-equity deal. And earlier this summer U.S. private-equity firm Carlyle Group teamed up with Italy's Finmeccanica to buy FiatAvio SpA, Fiat Group's aerospace business, for about 1.5 billion euros ($1.62 billion).

A Suez spokesman in New York said it isn't the company's policy to comment on what he termed "rumors."

Wall Street Journal Staff Reporters Anita Raghavan, Henry Sender and Robin Sidel contributed to this report.