NATO defence ministers are to meet on Thursday after a fresh showdown with Russia that saw Kremlin envoys to the alliance stripped of accreditation and NATO's office in Moscow set for shuttering.

The diplomats in Brussels were undeclared Russian intelligent officers, NATO said, leaving open what exactly they had allegedly done but pointing to a sustained pattern of disruptive activities. In response, Russia said it would suspend Moscow's NATO representation since the alliance clearly didn't want dialogue.

The western alliance's dealings with its traditional adversary Russia have grown increasingly strained since Moscow's 2014 annexation of Ukraine's Crimea. Russia in turn has repeatedly flagged the stationing of NATO forces near its territory.

The dispute isn't officially on the agenda at the ministers' talks in Brussels, which end Friday. Instead, the 30 allies are to discuss shared deterrence and defence strategy, investment in new technologies - including plans for a roughly 1-billion-euro (1.2-billion-dollar) fund - plus developments in Afghanistan.

NATO's almost 20-year military occupation in Afghanistan came to a calamitous end in August, when the militant Islamist Taliban group quickly retook power.

As well as ongoing efforts to evacuate staff, the allies are currently reviewing what lessons can be learned from the mission. They're also concerned the country could once again be used by other groups to launch terrorist attacks on western nations, and are mulling counter-terrorism options.

dpa