Doctors in the American city of Baltimore stopped a potentially life-threatening operation to separate the German Siamese twins Lea and Tabea after running into complications early Sunday morning. The doctors said they would first make a decision about whether to continue the procedure in several days. The 1-year-old twins are connected at the head, and doctors say the twins have a 50 percent chance of surviving the operation. A report in the newsweekly Stern said doctors were optimistic they could resume the operation within 72 hours.