Pfizer Inc. (NYSE: PFE) and Allergan plc agreed to terminate their $160 billion merger, an abrupt end to the largest-ever health-care acquisition as officials in Washington crack down on corporate inversions.

The U.S. Treasury Department’s proposed new rules to deter inversions drove the decision, the companies said Wednesday in a statement. New York-based Pfizer will pay Allergan $150 million in reimbursement for expenses associated with the transaction.

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