U.S. President Barack Obama said Thursday the change in command of U.S. troops in Afghanistan won't change the administration's policy in the war, and the war will enter a transition phase next year.

Obama said Gen. David Petraeus, commander of the Central Command who he tapped to take over the war effort in Afghanistan, "will not miss a beat" in carrying out the administration's war policies.

Petraeus "understands the strategy because he helped shape it," Obama said.

Obama on Wednesday accepted the resignation of Gen. Stanley McChrystal, who commanded all U.S. troops in the Afghan theater, and nominated Petraeus to step in. McChrystal was ousted because of disparaging remarks he made in a magazine article towards Obama and the administration's senior security officials.

Earlier Thursday, Defense Secretary Robert Gates also said the personnel change did not reflect any shift in strategy or in the administration's commitment to the war, while offering his full support to Obama's decision.

Answering a reporter's question in the White House, Obama said the Afghan war will enter a transition phase next year, as scheduled, but stressed July 2011 is just the beginning of the transition phase of U.S. Afghan strategy, it does not mean a sudden and complete withdrawal of U.S. military from that country.

Announcing the decision to send 30,000 additional troops to Afghanistan late last year, Obama promised to begin the pullout in July 2011.