PENTAGON - The Pentagon is not ready to move forward with President Donald Trump's new strategy for the war in Afghanistan, since military officials say key decisions have yet to be made.

Defense officials said Monday that critical planning was still under way, and that there was no timeline for when it might be finished, despite the fact that the Afghanistan strategy remains a "top priority."

"We're just not there yet," a Pentagon spokesman, Colonel Robert Manning, told reporters. "There is work to be done here within the department and answers that need to be provided."

Following months of deliberations, the president unveiled his new, "condition-based approach" for Afghanistan at a military base outside Washington last week.

"Conditions on the ground, not arbitrary timetables, will guide our strategy from now on," Trump told about 2,000 troops at Joint Base Myer.

President Donald Trump speaks at Fort Myer in Arli FILE - President Donald Trump speaks at Fort Myer in Arlington Va., Aug. 21, 2017, during an address to the nation about a strategy he believes will best position the U.S. to eventually declare victory in Afghanistan. FILE - President Donald Trump speaks at Fort Myer in Arlington Va., Aug. 21, 2017, during an address to the nation about a strategy he believes will best position the U.S. to eventually declare victory in Afghanistan.

The president offered few details about how many additional troops would be required in Afghanistan, or how they would support Afghan forces fighting both the Taliban and the Islamic State terror group.

"America's enemies must never know our plans or believe they can wait us out. I will not say when we are going to attack, but attack we will," Trump said.

Sources speaking to VOA on condition they not be named said up to 4,000 more U.S. troops could be sent to Afghanistan under the new strategy.

And the top U.S. commander for the region, General Joseph Votel, told reporters last week that the first of those troops would be arriving "pretty quickly," in a matter of days or weeks.

But while he refused to contradict Votel, spokesman Manning appeared to walk back the timeline for sending reinforcements.

"We're approaching this very deliberately," Manning said. "Once the chairman [of the Joint Chiefs of Staff] provides the recommendations, the secretary will determine how to move forward and how many additional troops we'll need to send."

Manning's comments Monday seemed to reflect an ongoing back-and-forth discussion among U.S. officials about how to proceed on Afghanistan.

Defense Secretary James Mattis attends a news conf FILE - Defense Secretary James Mattis attends a news conference, Aug. 17, 2017, at the State Department in Washington. FILE - Defense Secretary James Mattis attends a news conference, Aug. 17, 2017, at the State Department in Washington.

Earlier this month, prior to Trump's Afghanistan speech, Defense Secretary Jim Mattis seemed to suggest that most of the planning was done, and that it was simply a matter of deciding which approach would be best.

"We're sharpening each one of the options so you can see the pluses and minuses of each one, so that there's no longer any new data you're going to get. Now [we should] just make the decision," Mattis told Pentagon reporters August 14.

But following Trump's address, Mattis said he was waiting on the top U.S. military officer, Joint Chiefs Chairman General Joseph Dunford, to get him a plan "right away."

"We've obviously been discussing this option for some time," Mattis said during a visit to Iraq last week. "When he brings that to me, I'll determine how many more [troops] we need to send in."

One of the challenges for Pentagon planners is to determine exactly how many troops the U.S. has in Afghanistan.

Officials have put the number at about 8,400, tasked with carrying out counterterrorism operations against groups such as the Taliban or the IS Afghan affiliate. But that figure does not necessarily account for temporary support personnel or for defense contractors.

Military officials say the new plan for Afghanistan, once formed, may require reorganizing some forces already on the ground.

VOA's Steve Herman and Cindy Saine contributed to this report.