Germany's president apologized Thursday for failing to disclose that he took a much-criticized private loan, seeking to stem a persistent controversy that has raised questions over his authority.

Following days of silence in which he communicated mostly through his lawyers, President Christian Wulff had faced mounting calls from the opposition to make a personal statement on the affair.

Critics said he needed to do more to explain a euro500,000 ($650,000) loan he received in 2008 from the wife of a wealthy businessman and friend, apparently at below market rates, when he was governor of Lower Saxony state. He used the money to buy a house; German media reported on the loan last week.

Months before he became president last year, regional opposition lawmakers asked Wulff if he had business relations with longtime friend Egon Geerkens, a former jeweler and investor. He said he hadn't, but didn't mention the loan from Geerkens' wife.

"It has become clear to me how irritating the effect of the private financing for our house was in public," Wulff said in a hastily arranged statement to reporters at the president's Bellevue palace.

"I could and should have avoided that," he added. "I should have disclosed the private loan to Lower Saxony's Parliament back then ... I am sorry for that."

The president's lawyers Sunday also released a list of vacations Wulff spent at the homes of the Geerkens and other wealthy friends during his time as governor. The lawyers said his holidays "had no relation to his public offices" and broke no rules.

Prosecutors in Lower Saxony's capital, Hannover, said Thursday they received several complaints against Wulff alleging corruption in connection with the loan and the vacations, but found no evidence of any criminal offense and wouldn't open an investigation.

Still, Germany's largely ceremonial president is supposed to serve as a moral authority, and critics have raised questions over Wulff's integrity and judgment.

"I appreciate that not everything that is legally legitimate is also correct," Wulff said. However, he added: "personal friendships are important to me, but they have not influenced my conduct in office."

Wulff said he had dismissed his spokesman, Olaf Glaeseker, who previously served him in Lower Saxony. He didn't give a reason.

He said that he would continue to work "scrupulously and with all my strength" as president.

Wulff was Chancellor Angela Merkel's candidate for the presidency and before that a deputy leader of her conservative party. Merkel and her party have defended Wulff strongly. Any resignation would be embarrassing and distracting for the chancellor as she tries to tame the eurozone debt crisis.

Wulff replaced Horst Koehler, another Merkel nominee, last year after Koehler unexpectedly resigned _ citing criticism over comments he made about the German military.

"It is good that the president has broken his silence," said Hubertus Heil, a senior lawmaker with the opposition Social Democrats. But he added that "all legal doubts must be dispelled as soon as possible."