HATTIESBURG, Miss. -- Three days after a conference call with Packers team officials in which quarterback Brett Favre emphatically expressed his desire to play in 2008, Favre on Friday formally asked by letter for his unconditional contractual release, sources close to Favre and the team said.

The letter was sent by Favre's agent, James "Bus" Cook, via overnight mail on Thursday and arrived at the Packers facility Friday morning.

Cook, on behalf of Favre, expressed a desire to have an amicable parting, as the Packers have been reluctant to embrace his return. Favre announced his retirement in early March.

Packers general manager Ted Thompson and coach Mike McCarthy weren't available for comment Friday.

In a statement, the Packers said: "Brett earned and exercised the right to retire on his terms. We wanted him to return and welcomed him back on more than one occasion.

"Brett's press conference and subsequent conversations in the following weeks illustrated his commitment to retirement," the news release added. "The finality of his decision to retire was accepted by the organization. At that point, the Green Bay Packers made the commitment to move forward with our football team."