NATO could keep 8,000 to 12,000 troops in Afghanistan to train and assist the local police and military after the allied combat operation ends in late 2014, US Defence Secretary Leon Panetta said Friday.
"What we discussed was a range of options," Panetta said after a meeting of the 50 nations participating in the NATO-led International Security Assistance Force.
He stressed that no decision had been taken.
German Defence Minister Thomas de Maiziere had earlier created confusion by saying Panetta had "officially announced" a US involvement of around 8,000 to 12,000 troops in the post-2014 mission.
"That report is not correct," Panetta said. "The range of options we were discussing was with regards to the NATO force."
Afghan Defence Minister Bismillah Khan Mohammadi confirmed that the ministers had discussed overall figures. "This is just a thought, there is no final decision on it."
Diplomats said the US would likely provide around two thirds of the contingent.
NATO Secretary General Anders Fogh Rasmussen said the post-2014 mission would be "significantly smaller in size" than current one, and that a "regional approach" was planned.
De Maiziere in a statement said: "I expressed myself ... not clearly, by attributing the figures solely to the Americans."
It was not the first time NATO's Afghan operation created confusion among ministers attending talks in Brussels. Top US, Australian and NATO officials have had to clarify statements interpreted as signalling early ISAF troop withdrawals.
However the issue has been high on the minds of many among NATO's 28 members, who are eager for indications from Washington on the size of the post-2014 Afghanistan mission, named Resolute Support.
"We are all depending on the US decision," said Danish Defence Minister Nick Haekkerup upon arrival Thursday for the two-day meeting.
De Maizere had also been calling for more clarity from Washington, stating that "the time-frame is short between February 2014, until when we now have clarity, and after January 1, 2015."
A clearer message was delivered on new proposals to maintain 352,000 Afghan soldiers and police in the country through 2018, an option that Panetta said was "seriously being considered" by US President Barack Obama.
It remains unclear how the higher Afghan troop numbers would be funded, but Panetta appeared confident that Washington would approve the spending increase, despite looming defence cuts, saying it was an "investment that would be worth making."
Rasmussen has said it is "less expensive to finance Afghan security forces than to deploy foreign troops."
Earlier Friday, the defence ministers met their new Ukrainian counterpart Pavlo Lebedev, who pledged to provide a frigate and a helicopter to the alliance's anti-piracy operation in the Indian Ocean.
While praising Kiev's contributions to NATO missions in places such as Afghanistan, Rasmussen called on Ukraine to respect democracy and the rule of law.
"The determined implementation of reform to reinforce democracy and the rule of law would benefit the people of Ukraine and the whole Euro-Atlantic community," Rasmussen said.