Fresenius has more than 1,800 outpatient dialysis clinics in the United States that serve some 130,000 patients while Liberty has 260 dialysis centers that serve some 19,000 patients, the FTC said.

The FTC said the outpatient dialysis clinics to be sold were in 43 U.S. markets.

Fresenius, the world's largest dialysis company announced in August it would buy privately held Liberty for $1.7 billion, including $1 billion in debt.

Fresenius reported earnings and a 2012 outlook on February 21 that was slightly below expectations as it grappled with a new reimbursement system in the United States.

U.S. state-run insurer Medicare, which provides insurance for about 80 percent of FMC's U.S. patients, no longer pays for individual services and drugs but instead makes a lump-sum payment per dialysis session, as long as patients are kept in good health. Medicare guarantees access to health insurance for Americans aged 65 and older and some disabled people.

Fresenius has a U.S. market share of more than a third by patient numbers, with its closest rival, Davita Inc, commanding about a quarter.

Fresenius, which also makes dialysis machines, said on February 21 that net income in the fourth quarter rose 14 percent to $310 million, slightly below the average estimate of $316 million in a Reuters poll.

(Reporting By Diane Bartz; Editing by Tim Dobbyn)

• A Permanent Economic Emergency