US pressure for its allies to send more troops to Afghanistan and tension on Turkey's Iraq border are likely to dominate Nato talks in the Netherlands.
America supplies much of the air power in Afghanistan
Washington provides about half of the over 41,000 Nato troops in Afghanistan where resurgent Taleban militants are fighting in the south.
Turkey, which has the alliance's biggest European army, is poised to cross into Iraq in pursuit of rebels.
Defence ministers are gathering in the Dutch seaside resort of Noordwijk.
The talks were not originally scheduled to cover the crisis in Turkey, which has been fuelled by attacks by PKK Kurdish separatists based in northern Iraq.
The US and Turkey's allies have expressed solidarity but are also urging restraint, given the fragile stability established in the Kurdish north compared to the rest of Iraq.
Six years since the toppling of the Taleban there is an air of concern, if not crisis, about the Nato mission in Afghanistan, BBC defence correspondent Rob Watson reports.
As well as a Taleban revival, rebuilding has gone more slowly than expected and all of this has created strains among the Nato allies.
"I am not satisfied that an alliance whose members have over two million soldiers, sailors, marines and airmen cannot find the modest additional resources that have been committed for Afghanistan," US Defence Secretary Robert Gates said earlier this week.
There are disagreements over how much military force to use and some governments are under pressure to withdraw their troops from the mission.
But Nato defence ministers are expected to be asked to send more troops not so much for combat operations but to help train Afghanistan's own security forces.
Their improvement is now seen as the key to an eventual withdrawal of Western soldiers.
Nato officials accept the alliance may have its divisions over tactics, but insist that all members remain agreed that failure in Afghanistan is not an option, our correspondent adds.