BRUSSELS: World leaders are expected to agree at the NATO summit in Warsaw next month to maintain the alliance's broad geographic layout of bases in Afghanistan, a NATO diplomat said, a move that could make it easier for the United States to keep more troops there.

President Barack Obama plans to slash the number of US forces in Afghanistan from about 9,800 to 5,500 before he leaves office in 2017, despite calls from former commanders and envoys to halt the drawdown in the face of a renewed Taliban insurgency.

NATO allies are also signalling a willingness to stay, with Britain's Defense Secretary Michael Fallon saying flatly during a gathering of NATO ministers in Brussels: "This the wrong time to walk away from Afghanistan."

The NATO diplomat, speaking on condition of anonymity, declined to speculate on whether Obama might reconsider his withdrawal plans but said the decision on bases expected at Warsaw would take into account the slated US drawdown.

The United States contributes 6,800 troops to NATO's training mission in Afghanistan, which will fall to 3,400 under the current plan, the diplomat said. Washington also carries out a unilateral counter-terrorism mission in Afghanistan.

NATO's "hub-and-spoke" model for troops training and advising Afghan forces extends well beyond the capital Kabul to allow an international military presence at regional hubs. But NATO policymakers had been examining whether it was possible to keep those posts open, even as force levels fall.

"What I’m forecasting is that three weeks from now, that process will result (in a decision), and we will still be in the hub and four spokes," the diplomat said.

"I believe we’ll have sufficient resources, and our military commanders have told us we’ll have sufficient resources, to stay in the basic posture."

The senior diplomat, speaking to a small group of reporters on condition of anonymity, also expected NATO leaders to agree to some $5 billion in funding to sustain Afghan security forces at the current levels through 2020.

The current NATO commitment to fund the Afghan security forces only extends through 2017.

The funding is based on maintaining a goal of 352,000 Afghan soldiers and police. The official roster currently includes about 320,000 members of the security forces, a US military commander said earlier this week.