The former German chancellor Helmut Kohl is reported to be in a critical condition in the intensive-care unit of a German hospital.

Kohl, 85, who served as chancellor between 1982 and 1998 and is known as the architect of German reunification, was admitted to the Heidelberg’s university hospital in south-west Germany following an operation on his intestines, according to Spiegel Online.

Neither his office nor the Christian Democratic Union (CDU) has responded to requests by German media for information about his condition. The hospital said his family might release a statement.

Kohl was initially admitted to the orthopaedic clinic of the same hospital for hip-replacement surgery on 4 May. Following that operation, he told the tabloid Bild: “I want to get home as soon as possible.”

He subsequently underwent intestinal surgery and, according to Bunte magazine, was unconscious for a long period after the operation. He had been due to go to Bavaria at the weekend for post-surgery rehabilitation, the magazine added.

Kohl, who was also one of the authors of the European single currency, oversaw the reunification of East and West Germany in 1990, and served first as chancellor of the former West and then of a reunited country.

Angela Merkel is viewed as Kohl’s former protege, with him referring to her as his Mädchen or girl. But their relationship disintegrated after Kohl was forced to resign as head of the CDU after it was revealed he had received cash payments from unknown donors.

Kohl, who has used a wheelchair for several years, has been cared for by his second wife, 51-year-old Maike Kohl-Richter.