Former German chancellor Helmut Kohl is doing "well under the circumstances" after undergoing two operations, his office said Tuesday, in response to alarming media reports about the health of the man who oversaw reunification.

Kohl, 85, had a hip operation in early May, which went well, and subsequently needed a further operation which prolonged his stay in hospital, a statement said, without specifying what the second operation concerned.

"Under the circumstances Dr Helmut Kohl is doing well," it added.

Media reports citing his entourage had earlier said that Kohl was in intensive care after undergoing surgery.

News outlet Spiegel Online and glossy celebrity magazine Bunte reported that the conservative elder statesman had an intestinal operation at the university clinic of Heidelberg.

Spiegel said Kohl had been in the intensive care ward for three weeks and was in a "critical" condition.

In early May, Bild newspaper had reported that Kohl had successfully undergone a hip replacement operation and quoted him as saying he wanted "to be home again as quickly as possible".

Kohl, who served a record 16 years as chancellor from 1982 until 1998, oversaw his country's peaceful reunification the year after the 1989 fall of the Berlin Wall and the end to the Cold War.

Chancellor Angela Merkel was seen as Kohl's protegee and he brought her into the cabinet in 1991, but she later turned against him when he became embroiled in a slush-funds scandal.

The affair is seen as having helped propel Merkel to the helm of the Christian Democratic Union party and later the country.

Kohl exited active politics in 2002 and has been recently confined to a wheelchair with his speech severely impaired after his jaw was paralysed in a fall.

One of the key architects of Europe's push towards unity, Kohl is a passionate European and has often argued that building an integrated Europe is crucial to ensuring that war will never again ravage the continent.

He published a book last year entitled "Out of Concern for Europe", in which he lashed out at his successors over their policies in Russia and on the euro.

In 2001, his wife Hannelore, with whom he had two sons and who had long suffered with an excruciating sunlight allergy, committed suicide.

In 2008, Kohl married economy ministry aide Maike Richter, 35 years his junior.

He survived the massive 2004 tsunami that wrought widespread death and destruction in southeast Asia and had to be evacuated from a beach resort in Sri Lanka.