U.S. President Barack Obama, at the White House in Washington, D.C., on Tuesday, said he is 'concerned' about the leak of thousands of secret documents about the war in Afghanistan. (Pablo Martinez Monsivais/Associated Press)

U.S. President Barack Obama says he is concerned about the leak of thousands of secret documents about the war in Afghanistan that were published by the website WikiLeaks, but he added that they do not reveal any new issues.

"While I'm concerned about the disclosure of sensitive information from the battlefield that could potentially jeopardize individuals or operations, the fact is these documents don't reveal any issues that haven't already informed our public debate on Afghanistan," Obama said during a statement in the Rose Garden of the White House on Tuesday.

They were Obama's first comments on the leaks.

Obama said the documents point to the same challenges that led him to review U.S. policy last fall.

On Sunday, WikiLeaks published nearly 77,000 documents, revealing new details about the war in Afghanistan, including the relationship of the Pakistani military with Afghan insurgents. The documents were written by soldiers and intelligence officers. WikiLeaks plans to publish another 15,000 soon, bringing the total released to 92,000.

U.S. Senator John Kerry, the chairman of the Senate's foreign relations committee, called the leak illegal but he downplayed its significance, saying the documents revealed little that was not widely known by U.S. officials.

"I think it's important not to overhype or get excessively excited about the meaning of those documents," Kerry said.

The senator said the files were mainly drawn from raw intelligence, not assessments of trends.

Kerry spoke at a committee meeting to discuss the prospects of negotiating an end to the war in Afghanistan.

Admiral Mark Mullen, the chairman of the Joint Chiefs of Staff of the U.S. military, said in Baghdad that the leaks "appalled" him. Mullen said "there is a real potential threat there to put American lives at risk."

The U.S. army is leading an investigation launched Tuesday into the leak. Pentagon spokesman Col. Dave Lapan said the criminal probe is meant to find the leak's source.

While the U.S. army has charged Bradley Manning, an army intelligence specialist, with leaking other material to the WikiLeaks website, Lapan said it is not known if Manning was the source of the documents in the latest leak.

With files from The Associated Press