Defense Secretary Leon Panetta has refused to approve the transfer of five Taliban detainees from Guantanamo Bay to Qatar because the Gulf state is balking at imposing safeguards on their movements, say senior defense officials, casting doubt on U.S. hopes for negotiations to end the Afghan war.

Qatar has balked at U.S. demands that it take steps to ensure the detainees can´t leave the country after they are handed over, said the officials, who were briefed on the negotiations.

U.S. officials said the negotiations with Qatar were continuing and that sticking points could still be resolved. But the Pentagon has now taken the lead from the State Department in the negotiations with Qatar, officials said.

"The last thing the secretary wants to do is write condolence letters to service members killed as a result of anyone being returned to the battlefield," a senior military official said. Qatari officials in Doha and Washington couldn´t be reached to comment.

The insurgents say the transfer, part of a prisoner exchange pact under discussion, is necessary for peace talks to proceed.

The Taliban last week said they were suspending negotiations with the U.S., accusing Washington of failing to make good on the transfer and other commitments.

A senior Taliban commander who says he is in contact with Taliban negotiators said the cutoff was temporary, and only meant to address public anger in Afghanistan over the killing of 16 Afghan civilians, allegedly by a U.S. soldier.

"The Taliban know that peace is the only way out of this crisis. They realize that it is in their best interests," said Syed Mohammed Akbar Agha, cousin of the Taliban´s main negotiator with the U.S., in an interview with The Wall Street Journal. "Taliban hostility to the U.S. won´t last forever. Sooner or later, we´ll be friends and have good relations with the U.S."

The Taliban see the permission to open a Taliban office in Qatar and the exchange of the five detainees for a Westerner held captive by the insurgents as the first two steps required to establish trust between the parties, Mr. Agha said.

While Mr. Agha isn´t an official spokesman for the insurgents, U.S. and Taliban officials concur that these measures have been the focus of U.S. contacts with the Taliban.

The U.S. has for months been privately pressing Qatar on the need for safeguards governing the detainees. A senior defense official said Qatar and the U.S. have reached broad understandings about the need for surveillance, but have yet to work out details about how that would be done.

The proposed transfers have become a political lightning rod in Congress, with some Republicans accusing President Barack Obama of trying to cut a deal with terrorists. Some fellow Democrats in Congress have broken with Mr. Obama and say it is premature to make any detainee transfers since the Taliban have yet to agree to negotiate directly with the Afghan government.

Administration officials and congressional supporters of the proposed detainee transfer deal say Mr. Obama is taking a chance on negotiations to try to bring an end to the war.

Defense officials said getting Qatar to agree to the safeguards is critical to muting criticism from lawmakers if the transfer is approved.

Some Republicans in Congress who have long opposed Mr. Obama´s call for closing the detention facility in Guantanamo say the detainees slated to be sent to Qatar are too dangerous to be transferred.

"We have a history here, where individuals we have released have gone back in battle against us," said Sen. Kelly Ayotte (R., N.H.), applauding Mr. Panetta´s stance. "This is really an issue of safety for us and our allies."

State Department officials and diplomats have been pushing to quickly close a deal with the Taliban. Some officials said Mr. Panetta´s insistence on safeguards has been a source of frustration. They also said it is his responsibility to weigh the risks of the deal.

Mr. Panetta´s stand on the detainee transfers may reflect his long- standing skepticism about prospects for Afghan-Taliban reconciliation, echoing doubts expressed by some military leaders who argue that more pressure is needed to sap the Taliban´s fighting spirit and to force the group to the negotiating table in a weaker position.

Still, Mr. Panetta has made clear he supports administration efforts to sound out the Taliban and is prepared to back the transfers provided Qatar agrees to the more stringent safeguards to prevent the detainees from leaving the country. "But until we have safeguards in place, we are not going to Roger up," a senior defense official said.

Mr. Agha said his cousin, Tayeb Agha, the main Taliban negotiator, has held talks with the U.S. in Germany and in a Gulf emirate other than Qatar. In those talks, he said, the U.S. demanded as a precondition that the Taliban denounce their links with al Qaeda.

This demand still stands, though Mr. Agha said the Taliban saw it, at this stage of the talks, as illegitimate.

Mr. Agha, who spent four years behind bars for organizing the kidnapping of United Nations officials in 2004, provided in a Wall Street Journal interview a rare glimpse of the Taliban´s goals in the negotiating process.

Setting up a Qatar office and the prisoner exchange are the first two steps required to establish trust, Mr. Agha said. Afterward, the Taliban aim to negotiate regional cease-fires, he said.

Mr. Agha said the group wants the establishment of an Islamic-minded regime, but doesn´t want to lead the government. "If there is a true Islamic government, they won´t fight against it," he said. The official Taliban position is that the group´s pre-2001 Islamic Emirate of Afghanistan remains the country´s only legitimate government.

—Charles Levinson, Habib Khan Totakhil and Margaret Coker contributed to this article. (Copyright © Dow Jones & Company, Inc.) 03/21/12)