Obama rejects Clark's comments, his campaign said.

(CNN) - Barack Obama formally rejected Gen. Wesley Clark's recent comments Monday that questioned whether the John McCain's military experience qualified him to be commander in chief.

"As he's said many times before, Senator Obama honors and respects Senator McCain's service, and of course he rejects yesterday's statement by General Clark," Obama spokesman Bill Burton said in a statement.

The comments came in an interview on CBS Sunday when Clark suggested McCain's experience as a prisoner of war did not alone provide the necessary experience to set the country's national security policies.

"I certainly honor his service as a prisoner of war. He was a hero to me and to hundreds of thousands and millions of others in the armed forces as a prisoner of war. And he has traveled all over the world. But he hasn't held executive responsibility," said Clark, a former NATO commander who campaigned for the Democratic presidential nomination in 2004.

McCain campaign manager Rick Davis told CNN the comments were "the lowest form of politics," and the Arizona senator himself expressed disappointment with the comments on Monday.

"I know that General Clark is not an isolated incident but I have no way of knowing how much involvement Sen. Obama has in that issue," he told reporters. "I know he has mischaracterized some of my statements in the past including our involvement in Iraq but I'll let the American people decide about that. "

Watch: McCain upset over Clark's comments

Responding to the Obama campaign's rejection of Clark's comments, McCain spokesman Brian Rogers said, "We've learned we need to wait and see what Senator Obama actually does, rather than take him at his word."

Meanwhile, in what appeared to be an attempt to soften Clark's comments, Obama said in speech Monday that "no one should ever devalue that service, especially for the sake of a political campaign, and that goes for supporters of both sides."

"We must always express our profound gratitude for the service of our men and women in uniform. Period. Full stop," Obama said.

Update, 8:40 p.m.: Gen. Wesley Clark (Ret.) issued the following statement Monday night:

"There are many important issues in this Presidential election, clearly one of the most important issues is national security and keeping the American people safe. In my opinion, protecting the American people is the most important duty of our next President. I have made comments in the past about John McCain's service and I want to reiterate them in order be crystal clear. As I have said before I honor John McCain's service as a prisoner of war and a Vietnam Veteran. He was a hero to me and to hundreds of thousands and millions of others in Armed Forces as prisoner of war. I would never dishonor the service of someone who chose to wear the uniform for our nation.

"John McCain is running his campaign on his experience and how his experience would benefit him and our nation as President. That experience shows courage and commitment to our country – but it doesn't include executive experience wrestling with national policy or go-to-war decisions. And in this area his judgment has been flawed – he not only supported going into a war we didn't have to fight in Iraq, but has time and again undervalued other, non-military elements of national power that must be used effectively to protect America But as an American and former military officer I will not back down if I believe someone doesn't have sound judgment when it comes to our nation's most critical issues."

Lieberman is a backer of McCain.

(CNN) - Sen. Joe Lieberman, the Democrat-turned-Independent who is a strong supporter of Republican John McCain's White House bid, suggested Sunday the United States will likely face a terrorist attack in 2009.

The controversial comments followed remarks by top John McCain adviser Charlie Black late last week that a terrorist attack leading up the the general election would probably help the Arizona senator's White House hopes.

Watch: McCain adviser apologizes for comments

"Our enemies will test the new president early," Lieberman told CBS Sunday. "Remember that the truck bombing of the World Trade Center happened in the first year of the Clinton administration. 9/11 happened in the first year of the Bush administration."

McCain and his supporters have long argued the presumptive Republican presidential nominee is better-suited to handle the country's foreign policy challenges than Barack Obama.

Watch: Lieberman touts McCain

"[McCain] knows the world," Lieberman said. "He's been tested. He's ready to protect the security of the American people."

But Lieberman, who served as the Democratic vice presidential nominee in 2000, distanced himself from Black's contention that a terrorist attack would boost McCain's chances of winning the Oval Office.

"Sometimes even the best of them say things that are not what they intended to say," Lieberman said. "Certainly the implications there I know were not what Charlie intended. And he apologized for it. Senator McCain said he didn't agree. And, of course, I feel the same way.

Lieberman, who calls himself an "independent Democrat," endorsed McCain in early December.