The German news agency DPA quoted the couple's lawyer Gernot Lehr on Monday as saying the Wulffs had separated at the weekend to live in separate homes in the Hannover area, where Wulff was Lower Saxony's state premier before becoming president in 2010.

The news comes in the closing phase of a key election on January 20 in Lower Saxony, where Wulff's successor as Christian Democratic Party (CDU) premier, David McAllister, is seeking re-election.

The vote for Hannover's parliament is widely seen as a gauge for Chancellor Angela Merkel's federal re-election hopes in September. She, like McAllister, heads a center-right cabinet that also includes Germany's Free Democratic Party (FDP), whose voter support in recent surveys has sunk under a crucial parliamentary threshold of five percent.

Earlier on Monday, Germany's mass circulation tabloid Bild had said the Wulffs were separating, quoting "high-ranking circles" within Merkel's CDU.

In September, publicist Bettina Wulff had published a book entitled "Beyond the Protocol" in which she wrote that she and her husband had sought professional counseling.

Bild said the couple had signed a separation agreement on Monday morning in Hannover. Their two sons, aged four and nine, would remain with Mrs Wulff in the family home at Grossburgwedel, just east of Hannover.

High for Merkel's conservatives

Merkel's CDU together with Bavaria's Christian Social Union (CSU) allied conservatives are jointly riding a five-year nationwide high of 41 percent, according to an ARD public television survey published last Friday and conducted by the pollster Infratest.

The center-left Social Democratic Party (SPD) - led by its chancellery candidate Peer Steinbrück - scored 29 percent nationwide. The SPD's prospective federal partner, the Green party, garnered 12 percent.

The survey showed the Left Party on six percent. The FDP led by federal economy minister Philipp Rösler, who also hails from Lower Saxony, and the relatively new Pirate party each trailed on 4 percent.

ipj/rc (dpa, dapd)