WASHINGTON (CNN) -- White House spokesman Tony Snow called outgoing British Prime Minister Tony Blair "an extraordinary leader" Thursday, and said the president appreciates "everything he has done."

"He and the president are strong friends and allies but also the prime minister has demonstrated the ability to work with presidents of both parties and maintain a long tradition of an alliance that is of extraordinary strategic importance and we certainly appreciate everything he has done," Snow said in an off-camera press conference. "But furthermore, the fact is that he plans to have a very active schedule up to the very end and we plan to work with him each and every month."

Earlier Thursday, Blair announced he would formally submit his resignation to the queen on June 27. Britain's powerful finance minister, Gordon Brown, is the favorite to succeed Blair as Labour leader and prime minister.