* Angry Karzai says to stay out of talks
* Taliban flag and banner in Doha stir controversy
* U.S. secretary of state to travel to Qatar this week
* Four American soldiers killed in attack on Bagram base
Revived Afghan peace talks hit their first roadblock on Wednesday, a day after they were announced, as Afghan President Hamid Karzai said his government would not join U.S. talks with the Taliban and would halt negotiations with Washington on a post-2014 troop pact.
The United States and the Taliban had announced on Tuesday that officials from both sides will meet in Doha, the capital of Qatar, in coming days, in a step forward for a stuttering peace process after 12 years of bloody and costly war between U.S.-led forces and the insurgents.
But the precise timing of the negotiations was uncertain on Wednesday as U.S. officials worked furiously to keep the nascent peace talks on track.
Officials of Karzai's government, angered by the opening of a Taliban political office in Doha on Tuesday, said the United States had violated assurances it would not give official status to the insurgents.
"As long as the peace process is not Afghan-led, the High Peace Council will not participate in the talks in Qatar," Karzai said in a statement, referring to a body he set up in 2010 to seek a negotiated peace with the Taliban.
Karzai's objections appeared to focus on the way the Taliban unveiled the office in Doha, which suggested the Islamic movement would use it as an official embassy or even a base for a government-in-exile.
When Taliban envoys appeared at the building on Tuesday, it was decorated with a banner referring to the Islamic Emirate of Afghanistan, the name the Taliban used during its 1996-2001 rule of the country.
Karzai said the office's opening showed the United States had failed to honour promises made to the Afghan state about its role.
"The U.S. officials told us the office will be used to move peace talks forward, but not to give them an identity," an Afghan official said. "The Taliban's flag and the banner of the Islamic Emirate was something we did not expect."
U.S. and Afghan officials said U.S. Secretary of State John Kerry spoke with Karzai on Tuesday night and again on Wednesday morning in an effort to defuse the controversy.
Kerry told the Afghan leader that "the government of Qatar has taken steps today to ensure that the political office is in compliance with the conditions established by the government of Qatar for its operations," State Department spokeswoman Jen Psaki said.
Qatar "has had the sign with the incorrect name in front of the door taken down," Psaki said.
U.S. Defense Secretary Chuck Hagel, answering questions after an address on Wednesday at the University of Nebraska, said the involvement of Karzai's government would be essential for future talks.
Without specifying a time frame, Hagel added: "Any kind of a next set of meetings that would involve the United States - certainly we're a long way from any negotiations - would require the Taliban to agree to certain things. That can't be done, won't be done, without President Karzai and the people of Afghanistan."
Meanwhile, U.S.-Taliban talks that U.S. officials had suggested would take place in Doha on Thursday appeared to be delayed by at least a few days.
A senior U.S. official, speaking on condition of anonymity, said the initial meeting was likely to be held in the "next few days," but would not be more specific.
The dispute over the Taliban office after months of behind-the-scenes diplomacy to restart the peace talks underscored what U.S. officials say is a void of trust between Karzai and the Taliban, who have been waging an insurgency to overthrow his government and oust foreign troops.
Fighting continued in the war-ravaged nation. Four U.S. soldiers were killed in a rocket attack on the heavily fortified Bagram base near Kabul late on Tuesday, international military officials said.
TROOP TALKS SUSPENDED
Karzai's office also said it was suspending the talks on a post-2014 security pact with the United States.
Negotiations on the Bilateral Security Agreement began this year and, if completed, will set out how many U.S. bases and soldiers will remain in Afghanistan once NATO ends combat operations by December 2014.
"In view of the contradiction between acts and the statements made by the United States of America in regard to the peace process, the Afghan government suspended the negotiations," Karzai's office said in a statement.
"The suspension of the talks will continue until there is clarity from the United States," the Afghan official added.
The announcement of the diplomatic moves on Tuesday had raised hopes that Karzai's government and the Taliban might enter their first-ever direct negotiations on Afghanistan's future, with Washington acting as a broker and Pakistan as a major outside player.
On Tuesday, Karzai had said his government would also send a team to Qatar but added the talks should quickly be moved to Afghanistan.
The Taliban has until now refused talks with Kabul, calling Karzai and his government puppets of the West. But a senior Afghan official said earlier the Taliban were now willing to consider talks with the government.
It remained to be seen how long Karzai's boycott of the peace process - of which he is said to be deeply sceptical - will last. He has at times staked out stark positions publicly, only to reverse himself later.
A Taliban spokesman in Qatar on Wednesday confirmed the insurgency movement would attend a meeting with U.S. officials, but gave no time for the talks. The spokesman, Mohammed Naeem, told Reuters that no Afghan government officials would be at that meeting.
Underlining the importance of the process to the United States, the State Department said Kerry would travel to Doha for meetings with senior Qatari officials on Friday and Saturday. But U.S. officials said he would not meet with Taliban representatives.
SIGN OF OPTIMISM
The Taliban has said it wants a political solution that would bring about a just government and end foreign occupation of Afghanistan.
The first signs of optimism in peace efforts for many months come as the U.S.-led war effort reaches a critical juncture. The NATO command in Kabul on Tuesday handed over lead security responsibility to Afghan government forces across the country.
U.S. officials said that in the talks in Doha, the United States would stick to its insistence that the Taliban break ties with al Qaeda, end violence, and accept the Afghan constitution, including protection for women and minorities.
Asked if the Taliban would renounce al Qaeda, which Washington considers a terrorist organization, Naeem, the Taliban spokesman, said there was no clear definition of terrorism.
"Once we define what terrorism is, for the Islamic emirate of Afghanistan (the Taliban), (we) will be able to say what is acceptable and what is not acceptable," he said.
The Taliban is expected to demand the return of former senior commanders now detained at the U.S. military prison at Guantanamo Bay, Cuba, a move opposed by many in the U.S. Congress, as well as the departure of all foreign troops.
The United States wants the return of the only known U.S. prisoner of war from the conflict, Sergeant Bowe Bergdahl, who is believed to be held by the Taliban.