By Mark Felsenthal, Hamid Shalizi and Dylan Welch WASHINGTON/KABUL (Reuters) - The United States will meet the Taliban this week for talks aimed at achieving peace in Afghanistan, where U.S.-led forces and the insurgents have fought a bloody and costly war for the past 12 years, U.S. officials said on Tuesday. A senior U.S. official said the talks would start in Doha on Thursday, but President Barack Obama cautioned against expectations of quick progress, saying the peace process would not be easy or quick. U.S. officials said the process could take many years and be subject to reversals. U.S. officials say they hope the meeting will open the way for the first-ever official peace talks between the government of Afghan President Hamid Karzai and the Taliban, which has waged a 12-year campaign to oust him and foreign troops. The Taliban have until now said they would not countenance talks with the government, which they consider a stooge of the United States and other Western states in the NATO coalition fighting in Afghanistan. News of the planned talks comes as the United States and its allies in NATO seek to meet a deadline of December 2014 for an end to foreign combat operations in Afghanistan. This would allow them to withdraw the majority of their troops and wind down an engagement launched after the September 11 attacks on the United States in 2001 that has cost hundreds of billions of dollars and tens of thousands of lives. For its part, the Taliban is expected to demand the return of prisoners now at the U.S. military prison at Guantanamo Bay in Cuba - a move many in the U.S. Congress oppose - as well as the departure of all foreign troops. The United States says it hopes to keep a force, of as yet undetermined size, in the country after the end of the NATO combat mission. The talks will be the first U.S. meeting with the Taliban in several years. U.S. officials said the initial meeting was expected to involve an exchange of agendas, followed by another meeting a week or two later to discuss next steps. Obama said peace would only come through an Afghanistan-led process, and commended Karzai for taking a courageous step toward peace. He stressed that the U.S. military effort would continue in spite of the peace efforts. We don't anticipate this process will be easy or quick but we must pursue it in parallel with our military approach. And we in the meantime remain fully committed to our military efforts to defeat al Qaeda and to support the Afghan national security forces," Obama said. Despite the accompanying words of caution, the announcement of the planned talks represents a significant step forward in the peace process, which has struggled to achieve results despite years of attempts. Tiny, gas-rich Qatar has been an enthusiastic supporter of reconciliation efforts in a number of crises affecting the Muslim world including those in Afghanistan, Yemen, Somalia, Lebanon and Darfur, often hosting peace talks on its own soil to try to prove it can punch above its weight in diplomacy. A U.S. official said the talks would be conducted on the Taliban side by its political commission, with the authorization of Mullah Omar, and also represent the al Qaeda-linked Haqqani network. The Haqqanis are considered the United States' deadliest foe in Afghanistan and the top U.S. and NATO commander in the country cast doubt on Tuesday over whether it could make peace. "All I've seen of the Haqqani would make it hard for me to believe they were reconcilable," U.S. General Joseph Dunford told Pentagon reporters by phone from Kabul. U.S. officials said they expected detainee exchanges to be discussed in the talks. The United States will ask for the safe return of U.S. Sergeant Bowe Bergdahl, who has been a prisoner since June 2009, the officials said. He is thought to be being held by Taliban militants in northwestern Pakistan. Additional reporting by Mirwais Harooni in Kabul, Saud Mehsud in Dera Ismail Khan, William Maclean, Amena Bakr and Yara Bayoumy in Dubai, Jeff Mason in Enniskillen and Warren Strobel and Phil Stewart in Washington; Writing by David Brunnstrom; Editing by David Storey and Jim Loney