NATO expects to have an interim rapid-reaction force in place by next year to deal with new security challenges in Europe and elsewhere, the alliance's secretary-general said Monday.

Jens Stoltenberg said the force would be a provisional step until a full-scale unit can be organized in 2016.

Stoltenberg said Germany, Norway and the Netherlands have agreed to contribute troops to the initial force. The bigger rapid-reaction force was agreed to at a NATO summit in September as a response to Russian actions in Ukraine.

The NATO chief met with reporters to preview the agenda of Tuesday's meeting of alliance foreign ministers in Brussels. U.S. Secretary of State John Kerry is scheduled to attend the session, which will cover a broad range of issues, from reviewing actions taken by NATO since the September summit in Wales to NATO's planned non-combat mission in Afghanistan starting Jan. 1.

On Wednesday, Kerry will chair a separate meeting at NATO headquarters of countries involved in the campaign against the Islamic State extremist group.

Douglas Lute, U.S. ambassador to NATO, said the prototype of what's officially called the High Readiness Joint Task Force will be used as a "test bed" to gauge its command and control, logistics, sustainability and connections with host nations and NATO's supreme commander in Europe.

The goal is to hone response time throughout 2015 so the unit will be able to deploy within days, Lute said.

The actual size and composition of the force is expected to be set by NATO defense ministers in February. Lute said many questions about it still remain to be answered, not least how it will be paid for.

Stoltenberg said the interim unit's creation proves NATO is moving faster to beef up security than foreseen at the Wales summit.