NATO foreign ministers meet in Brussels on Tuesday to chart a course forward after a "year of aggression" from Ukraine to the Middle East and the end of the alliance's combat mission in Afghanistan.

New chief Jens Stoltenberg said on the eve of the meeting that it was a decisive time marked by Russia's intervention in Ukraine and the regional threat from the Islamic State jihadist group in Iraq and Syria.

"2014 has been a year of aggression, crisis and conflict," said Norway's Stoltenberg, who took over from Denmark's Anders Fogh Rasmussen on October 1, adding that "Russia's actions have undermined Euro-Atlantic security."

US Secretary of State John Kerry and other ministers will tackle an agenda topped by an interim rapid-reaction force capable of meeting the new and more unpredictable threats that the transatlantic alliance faces.

Accustomed to long-term challenges, NATO's 28 leaders accepted at a September summit they now faced a different world where hybrid warfare and political upheaval defied traditional military solutions.

In September they agreed on a "spearhead" force estimated at around 4,000 troops to be ready by 2016, but on Tuesday they will discuss an even faster, smaller force to be ready by early 2015, with Germany and the Netherlands willing to contribute troops.

"This will make us even better prepared to deter and to defend against any crisis arising around our borders," Stoltenberg said.

Ministers will also review NATO efforts to reassure eastern members such as the Baltic states and Poland -- once ruled from Moscow -- by rotating aircraft, ships and troops through the region to demonstrate its commitment to their defence.

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For Ukraine itself, the foreign ministers are expected to approve four trust funds to finance its military modernisation, as government forces battle pro-Kremlin rebels in the east in a conflict which has claimed more than 4,000 lives.

Stoltenberg also called for Russia to reduce its military build-up on Ukraine's borders.

But the question of NATO membership will be strictly off limits, diplomatic sources said.

Kiev's new government wants to restart the membership process interrupted by ousted leader Viktor Yanukovych, but President Vladimir Putin's Russia fiercely opposes it.

"We want to avoid talking about that," one source told AFP, adding: "Nobody thinks it is a good idea; it risks making things worse rather than calming them down."

The US ambassador to NATO, Douglas Lute, said separately on Monday that the alliance did not solicit new members and it was first of all up to an individual country to apply for membership, setting in train a lengthy admission process.

Ministers close the meeting Tuesday in the presence of new Afghan President Ashraf Ghani and chief executive Abdullah Abdullah as the alliance's longest ever combat operation ends in a few weeks.

NATO will replace it with a training and advisory force of some 12,500 troops, mostly US.

Ghani told Stoltenberg Monday that this new partnership was based on a shared interest and that Europe and North America had been made safer by the war against the Taliban, who were ousted in 2001 by US-led forces after the 9/11 terror attacks.

Many of the foreign ministers return again Wednesday to NATO HQ in Brussels but this time with Kerry in the chair for a meeting of the 60-strong US-led coalition against IS.

NATO has said it is willing to assist Iraq if it requests help in boosting its military capacity but Stoltenberg stressed that the alliance has no direct role to play in the conflict, with military support strictly a bilateral matter for individual countries.