BRUSSELS (AP) — As rising violence threatens to derail Afghan peace talks, the head of NATO said Wednesday that the military alliance will not leave Afghanistan until security conditions allow, even as some U.S. troops might be hoping to be back home in time for Christmas.

“We will make a decision together, coordinate our efforts based on the principle ‘in together, adjust together, and when the time is right, when the conditions are met, then we will leave together,’ but not before,” NATO Secretary-General Jens Stoltenberg told reporters.

President Donald Trump tweeted on Oct. 7 that “we should have the small remaining number of our BRAVE Men and Women serving in Afghanistan home by Christmas.” The U.S. armed forces were blindsided by the claim, as were NATO allies.

NATO has led international security efforts in Afghanistan since 2003; two years after a U.S.-led coalition ousted the Taliban movement for harboring former al-Qaeda chief Osama bin Laden. Around 12,000 troops from 38 countries are now working in Afghanistan to train, mentor and assist the national security forces.

Americans often make up at least half of the troops participating in the mission, dubbed Resolute Support. Around 8,000 U.S. troops were involved as recently as August. NATO allies and their partners rely on U.S. air power, transport, logistics and medical assistance to operate. It’s unlikely that the mission could function without significant U.S. help.

Diplomats and military officers are concerned that setting a definitive date on any troop withdrawal from Afghanistan could hamper efforts to secure a peace deal between the Taliban and the Afghan government.

Confusion about troops movements in what is America’s longest war and NATO’s biggest and most challenging operation ever is also an extremely sensitive issue for the military personnel involved and their families.

Last week, Trump’s national security adviser said the number of U.S. troops would shrink to 2,500 early next year. He suggested that Trump’s tweet that all forces should be home by Christmas was more a wish than reality. U.S. commanders say the plan is to reduce the U.S. presence to 4.500 by November.

NATO diplomats expect troops to still be in Afghanistan until at least the middle of next year.

On Monday, the U.S. special envoy to Afghanistan warned that “distressingly high” levels of violence, notably in the Taliban stronghold of Helmand province. threaten to derail peace talks being held in the Qatari capital, Doha,

“The Taliban must live up to their commitments, significantly reduce the levels of violence, and pave the way for a ceasefire. They must break all ties with al-Qaeda and other international terrorist groups. And they must negotiate in good faith,” Stoltenberg said.

He said the peace talks “offer the best chance for peace in a generation. They must preserve the gains made at such high price over the last two decades, including for women and girls.”