(CNN) In an ongoing open rift among the most senior officials in the Trump administration, White House National Security Adviser Robert O'Brien seemingly took a shot Friday at the chairman of the Joint Chiefs of Staff, Gen. Mark Milley, following Milley's public skepticism about the White House's announcement that the US will aggressively reduce the number of troops in Afghanistan by the end of the year no matter what.
"The President has set a timeline for troop withdrawal; we are going to be down to under 5,000 troops within the next month, and in the early part of next year we're going to be down to 2,500 troops," O'Brien said Friday during his opening remarks at an event hosted by the Aspen Security Forum. "That has been suggested by some that that's speculation. I can guarantee you that's the plan of the President of the United States."
O'Brien added: "That's not speculation, that's the order of the commander-in-chief, the DOD is working on those plans and Secretary (Mark) Esper is fully on board and implementing them."
The Pentagon did not immediately respond to a question about O'Brien's comments, but the Department of Defense has long said that additional troop reductions in Afghanistan will be contingent on the conditions on the ground improving, and the Taliban's adherence to the agreement it signed with the Trump administration in February.
In an interview broadcast Monday, Milley had stressed that future troop reductions would be conditions-based, and responded forcefully to O'Brien's recent announcement that the US would cut troops to 2,500 irrespective of conditions on the ground.
"Robert O'Brien, or anyone else, can speculate as they see fit, I am not going to engage in speculation, I'm going to engage in the rigorous analysis of the situation based on the conditions and the plans that I'm aware of in my conversations with the President," Milley told NPR.
"That was the decision of the President on a conditions-based withdrawal," Milley added, saying, "The key here is that we're trying to end a war responsibly, deliberately, and to do it on terms that guarantee the safety of the US vital national security interests that are at stake in Afghanistan."
A defense official told CNN that Milley's remarks still reflected the US military's views on the situation.
In February, the Trump administration signed a historic agreement with the Taliban that committed the US to withdrawing its troops from Afghanistan by the spring of 2021 in exchange for the Taliban meeting a series of commitments, including entering into negotiations with the Afghan government and severing its ties with terrorist groups like al Qaeda.
And while Pentagon officials have said that the Taliban has yet to fully sever its ties to terrorists, the US has already substantially reduced the number of US troops in Afghanistan, drawing down from over 10,000 to 8,600 immediately upon signing the agreement and cutting troop levels to 4,500 despite continued Taliban attacks against the Afghan government.
Conditions on the ground appeared to be further deteriorating in recent days as the Taliban launched a major military offensive against the Afghan government in the capital of Helmand Province in the country's south despite ongoing peace talks in Qatar, an attack that prompted US military aircraft to carry out a series of airstrikes against Taliban fighters in recent days.
The attack by the Taliban on Helmand's capital of Lashkar Gah appeared to be a violation of the terms of its deal with the US, with Milley saying that the Taliban had agreed to not attack major urban areas.
On Thursday, the Trump administration's special envoy for the Afghan peace process, Amb. Zalmay Khalilzad, tweeted that following several meetings with the Taliban, the US and the Taliban "agreed to re-set actions by strictly adhering to implementation of all elements of the U.S.-Taliban Agreement and all commitments made."
The US government has offered no details as to what the "re-set" would entail, but Khalilzad said it would mean "reduced numbers of operations. At present too many Afghans are dying. With the re-set, we expect that number to drop significantly."
The future of the US military's involvement in Afghanistan remains clouded in uncertainty following contradictory comments from senior members of the administration.
Following O'Brien's comments last week that the US would reduce troops to 2,500, President Donald Trump tweeted that all US troops in Afghanistan "should" be home "by Christmas," an even more ambitious timeline.
"I think what the President was doing is he was expressing the same desire that I think every president since the Revolutionary War has said," O'Brien explained Friday, saying, "we want the troops home by Christmas."
"If these inter-Aghan negotiations could work out well there would be nothing greater than to have our troops home by Christmas," O'Brien added. "If the conditions permit it look we would love to get people out earlier and I think that's the desire the president was expressing."
The strategic confusion has been met with some criticism.
"The disarray at top levels of the administration and the President's push to withdraw troops because of the election are key reasons the Taliban continues its campaign of violence, ignoring the US-Taliban agreement terms," said former Pentagon spokesman and retired US Marine Corps Col. David Lapan.