(Bob Gathany/AP Photo)

President Obama had nothing but praise today for former Defense Secretary Robert Gates, despite his scathing critique of the president and Vice President Joe Biden featured in his upcoming book, "Duty."

"Secretary Gates was an outstanding secretary of defense, a good friend of mine and I'll always be grateful for his service," Obama told reporters after a meeting with Spanish Prime Minister Mariano Rajoy in the Oval Office.

The president opted not to comment on Gates' criticisms, instead noting that their work together on Afghanistan produced the "right strategy.

"As he notes, he and I and the rest of my national security team came up with a strategy for Afghanistan that was the right strategy, and we are continuing to execute," the president said. "I think that what's important is that we got the policy right but that this is hard, and it always has been."

"Just as I have continued to have faith in our mission, most importantly I've had unwavering confidence in our troops and their performance in some of the most difficult situations imaginable, and that job is not yet done," the president later added.

In his book, to be released Tuesday, Gates writes that President Obama lost faith in his Afghanistan strategy. He also issues a particularly brutal assessment of Biden's foreign policy acumen.

"I think he has been wrong on nearly every major foreign policy and national security issue over the past four decades," Gates writes.