Kai Eide, who stepped down in March after two years as the U.N.'s top official in Afghanistan, said there is typically a reduction in fighting in the winter months. And he said that could offer an opportunity to test whether the Taliban are ready to start talks.
"I believe there is a window to get started," Eide told The Associated Press in an interview.
"The time has come to accept that a reconciliation policy cannot be viable if you don't include the leadership of those movements," he said, referring to the Taliban.
Eide said a middleman is needed to facilitate such talks and he proposed the role be given to veteran U.N. diplomat Lakhdar Brahimi.
Many top military and diplomatic leaders have publicly supported peace efforts, though they remain skeptical that insurgents are ready to lay down their arms, embrace the Afghan constitution and sever ties with al-Qaida and other terrorist networks.
Eide criticized President Barack Obama's plan to start withdrawing U.S. troops in July 2011, saying "it stimulated the insurgency."
He also makes that argument in a book being released this week in Norway about his experiences in Afghanistan.
Obama's plan puts pressure on other countries with forces in Afghanistan to speed up their withdrawal, and signals to the Taliban that "Western patience is about to end," Eide wrote in the book.
In the preface, Eide wrote he increasingly disagreed with Washington's strategy in Afghanistan, saying it put too much emphasis on military operations over civilian reconstruction efforts.
"In my opinion it was a strategy being doomed to fail," Eide wrote.
He said U.S. Ambassador to Afghanistan Karl Eikenberry had also warned against an imbalance between military and civilian efforts. "But none of us gained support for our views," Eide wrote.
He was replaced by Swedish diplomat Staffan de Mistura as the U.N.'s top official in Afghanistan.