Magazine: Helmut Kohl in hospital

There was no immediate confirmation of Tuesday's report in "Bunte" from the clinic, the German government or the Christian Democratic Union (CDU) party, which Kohl had headed.

According to "Bunte," Kohl was unconscious for a long time following an operation on his intestine. German news website "Spiegel Online" reported that Kohl has been in intensive care for the past three weeks, citing an unnamed source close to Kohl.

Early in May, Kohl was reported to have undergone a hip operation in Heidelberg. At the time, he told German newspaper "Bild" that he would like to "return home as quickly as possible."

Helmut Kohl served as chancellor between 1982 and 1998 – first as chancellor of the former West Germany, then leading the country through its period of reunification.

Kohl - described in November 2014 as a "great European" by European Commission President Jean-Claude Juncker - is also credited with championing European unity and setting the euro currency into motion.

He turned 85 in April.

Current German Chancellor Angela Merkel is widely regarded as Kohl's former protégé, but the relationship between the two broke down following an expenses scandal in 1999 which saw Kohl toppled from his role as the head of the conservative CDU. It was revealed he had received cash donations from unknown sources.

More recently, he won legal victories against his one-time ghost writer Heribert Schwan, who had published a controversial memoir "Vermächtnis: Die Kohl-Protokolle" (Legacy: The Kohl Protocols) without Kohl's permission.

Kohl's own book – its title is literally translated as "Out of concern for Europe" was released in November 2014 and retraces the quest for peace after two world wars in 20th-century Europe and reasserts his belief in the common euro currency.

se/kms (dpa, Reuters)