White House press secretary Jay Carney on Tuesday declined to deny reports that President Obama will write a letter acknowledging U.S. mistakes in the Afghanistan war as part of a security agreement with Kabul.

Carney said he would not “comment on presidential correspondence." He addressed the issue of Afghan civilian casualties, however, and stressed that the U.S. worked carefully to avoid them.

“We take various precautions to prevent civilian casualties,” said Carney. He added that the U.S. “always expresses regret when civilians are killed.”

“It’s an issue we continue to work through,” he added, noting that “our concern about potential civilian casualties is reflected in the extreme care taken by our military forces.”

Carney’s comments came after Reuters reported that Obama would write a letter to the Afghan people, admitting that mistakes had been made in the “war on terror,” citing a spokesperson for Afghan President Hamid Karzai.

The report came as Afghan and U.S. negotiators worked toward a post-2014 security agreement between the two nations. NATO coalition troops are slated to leave in 2014, but the administration hopes to retain a residual force to continue to provide training for Afghan security forces and to help stabilize the country.

But the talks have been contentious, with Karzai wanting assurances that the U.S. would no longer have the authority to conduct raids on Afghan homes. Reports Tuesday said that the two sides were close to a deal that would allow U.S. raids in “extraordinary circumstances” only.

If both sides complete an agreement, it would need to be approved by the loya jirga, a council of Afghan elders.

Secretary of State John Kerry also spoke with Karzai by phone on Tuesday and left open the possibility of a letter from Obama.

Karzai asked for “reassurances that he could communicate to the Loya Jirga regarding the nature of our security relationship going forward and addressing past issues such as civilian casualties,” according to a senior State Department official.

“Secretary Kerry indicated that we want to continue working together to find a path forward, and that we will consider his request for reassurances including the option of a letter from the Administration stating our position,” the official added.

Carney on Tuesday stressed that any post-2014 U.S. presence would be drastically downscaled from the decade-plus-long American involvement in Afghanistan.

“The war in Afghanistan will end next year. The combat mission will be over,” said Carney.

This story was published at 2:47 p.m. and has been updated.

White House correspondent Susan Crabtree contributed to this story.