BERLIN - Visiting US President Barack Obama defended the country's internet surveillance programs on Wednesday, saying that lives have been saved and threats averted thanks to the monitored information.

Obama said during a joint press conference with German Chancellor Angela Merkel that at least 50 threats, both in the US and countries including Germany, had been averted because of information the National Security Agency (NSA) was able to access.

He assured the German public that the programs were subject to court oversight and followed strict procedures in order to prevent terrorist attacks.

Merke, meanwhile, said at the press conference that government monitoring of Internet communications needed to remain within proper limits, stressing the importance of proportionality and balance.

"I made clear that although we do see the need for gathering information, the topic of proportionality is always an important one," Merkel said, adding that the two sides will continue their discussion on the issue after agreeing to further exchange information.

Under a highly classified program disclosed by media recently, the NSA and the Federal Bureau of Investigation have been tapping directly into the central servers of nine US internet companies, enabling analysts to track a person's movements and contacts over time. Obama insisted that the surveillance program was purely aimed at thwarting terror attacks.

Merkel told broadcaster RTL in a recent interview that she was surprised by the program, saying that the German people wanted to know if their online data was being monitored by the US agency. She called for more transparency over the issue, which caused deep unease in the privacy-sensitive German society.

Obama is visiting Germany for the first time as the US president. The highlight of his visit will be a speech on Wednesday afternoon at the Brandenburg Gate, 50 years after John F. Kennedy made the famous "Ich bin ein Berliner" address at the same site.