WASHINGTON - US Defence Secretary Jim Mattis said Wednesday he is finalising recommendations for a new military plan for Afghanistan, but he still needs input from NATO allies.

The Pentagon is expected to request thousands of additional troops for Afghanistan in a bid to end chronic instability and snap a protracted stalemate against the Taliban. Any such proposal would ultimately need a green light from President Donald Trump.

"We are working on it and we will obviously engage quietly with our allies as we come to final decisions," Mattis said. "It's more important to get it right than do it hastily," he added, speaking briefly to reporters at a meeting with Norwegian Defence Minister Ine Marie Eriksen Soreide. Mattis's remarks may tamp down expectations that an Afghanistan announcement is imminent.

Theresa Whelan, the acting assistant secretary of defence for special operations, said on May 4 that she expected a Pentagon recommendation to go to Mattis "within the next week." US media have reported the Pentagon is weighing around 3,000 to 5,000 additional troops. US troops in Afghanistan number about 8,400 today, and there are another 5,000 from NATO allies, serving in an advisory capacity for Afghan forces.

Soreide suggested Norway might be willing to increase its own small-but-longstanding commitment to Afghanistan.

"We have always consistently said that we went in with our allies and we are going to leave with our allies. So depending on what NATO takes as their next step we will follow that discussion very closely," she said.  "Some time through the summer we will see that NATO also makes some decision on what to do next with the Resolute Support mission," she added, referring to the NATO operation in Afghanistan.

Trump, who campaigned on an "America First" platform and a pledge to reduce US overseas involvement, must decide whether to approve the expected request.

Such a move could prove a tough sell in America, which has seen about 2,400 troops killed in Afghanistan since 2001 and another 20,000 wounded.