WASHINGTON — Gen. David McKiernan was forced out as head of U.S. Forces in Afghanistan, a move Defense Secretary Robert Gates said was needed to find new ways to end conflict there.

"From a military perspective, we can and must do better," Gates said at a news conference Monday. "Our mission there requires new thinking and new approaches from our military leaders.

"We have a new policy set by our new president. We have a new strategy, a new mission, and a new ambassador. I believe new military leadership is also needed."

McKiernan will be replaced by Lt. Gen. Stanley McChrystal, who currently serves as director of the Joint Staff. Gates also announced the assignment of Lt. Gen. David Rodriguez to a new three-star post in Kabul, designed to help deal with day-to-day military operations in the country.

McKiernan will serve until McChrystal and Rodriguez are confirmed by the Senate. McKiernan also serves as commander of International Security Assistance Force (ISAF) forces in Afghanistan, a post he took over just 11 months ago.

Time Magazine recently highlighted McKiernan in their annual "World’s 100 most influential people" issue. In February he predicted a "tough year" of fighting for U.S. forces in the country, and warned the deployment of 30,000 new troops into Afghanistan might not be enough to continue progress past the end of this year.

Gates praised McKiernan’s service and said the change was not a negative reflection on his work.

"Nothing went wrong," Gates said. "There was nothing specific. It simply was my conviction … that a fresh approach and a fresh look in a context of the new strategy was probably in our best interest."

Anthony Cordesman, analyst at the Center for Strategic and International Studies, said the move shows the White House’s belief that the coming months are a critical period in the future of U.S. operations overseas.

"The deterioration of Afghanistan over the last year was certainly not (McKiernan’s) fault," he said. "But his experience is as a different kind of commander.

"He does not have the direct experience with the clear-hold-build strategy that McChrystal has. That’s what the White House and Gen. (David) Petraeus see needed there right now."

Kabir Sekander, a cultural adviser and translator for McKiernan, said Monday that McKiernan had told staffers just days before about the leadership change.

"It was very sad," Sekander said. "This guy honestly worked so hard and did so many good things. He was very involved in so many aspects of this job and the mission. We went with him to so many meetings with the elders. I traveled with him extensively all over the country.

"In my opinion, he was very successful."

But Sekander said he did not have plans to leave his post because of the shake-up. "For me, honestly, like General McKiernan told us, it’s no matter who is the commander. The mission is what’s important."

Daniel Markey, senior fellow at the Council on Foreign Relations, called the move shocking. "I was under the impression that McKiernan’s role was pretty firm here."

"His strategy has been consistent with what they want to do in Afghanistan," he said. "He’s been one of the main proponents of moving away from targeted counter-terror activities to a broader approach. There were no tensions that I knew of. So this really is a surprise."

Both Gates and Joint Chiefs of Staff Chairman Adm. Michael Mullen highlighted the new nominees’ experience in Afghanistan as a key reason for their appointments.

"Gen. McChrystal and Gen. Rodriguez bring a unique skill set in counterinsurgency to these issues," Gates said. "They will provide the kind of leadership we’ve been talking about."

McChrystal lead Joint Special Operations Command for nearly five years prior to assuming his current post. He will receive a fourth star upon taking over the Afghanistan role.

For the last month, he headed a task force focused on improving the effectiveness of the U.S. strategy in Afghanistan.

In 2007, McChrystal was the highest-ranking officer chastised by the Defense Department Inspector General in their investigation of Pat Tillman’s death, calling him "accountable for the inaccurate and misleading assertions" in the documentation for his Silver Star. However, investigators said they did not see evidence of a cover-up in that friendly fire incident.

Rodriguez serves as top military aide to Gates and previously commanded Combined Joint Task Force 82 in Afghanistan.

Reporter Nancy Montgomery contributed to this story.