NATO defence ministers meet Tuesday to review the alliance's costly commitments, most notably in Afghanistan, as slowing Western economies seriously undercut defence spending.

Afghanistan is the major talking point, to be taken up on Wednesday, officials said, with the alliance soon to start planning for its new training, advice and assistance mission after the 2014 withdrawal of combat troops.

The NATO-led peacekeeping force in Kosovo, whose self-proclaimed independence is disputed by neighbouring Serbia, is less dramatic but also requires discussion as the commitment runs into its 13th year.

Officials Monday highlighted the impact of the economic slump on defence spending, stressing the need for a common effort to make funds go further and the importance of joint operations and capabilities, as demonstrated in Afghanistan.

"If we wind down our combined operations, what can we do to maintain our inter-operability (which) is both a military requirement and a political one," one official said.

NATO agreed at a Chicago summit in May on a "2020" concept which gives a large role to "Smart Defence," the sharing of resources combined with more coordination.

The issue is fraught, however, as member nations jealously guard sovereignty in the all important matter of defence, though there seems to be little alternative to more burden sharing for all NATO members.

"Economic conditions in many countries have not got any better since Chicago... it is not realistic to think of large increases (in defence spending) at the national level," one official said.

A planned major tie-up between Britain's BAE Systems and EADS, the European aerospace giant, represents a massive pooling of European defence resources but officials said the deal was not on the agenda.

Ministers involved -- British, French, German and US -- would likely take it up separately, they added. BAE Systems have a large part of their business in the United States.

BAE and EADS have until Wednesday -- a British stock market deadline -- to formally go ahead, abandon or to ask for more time to finalise a deal which would form a company to more than rival US giant Boeing.

Officials said the Syria conflict will also feature amid mounting fatalities and tensions involving alliance member Turkey but the subject is not on the official agenda.

One senior NATO diplomat described the Syrian shelling which killed five people in a Turkish border village last week as "behaviour totally unacceptable" and stressed Ankara's status as a fully paid-up NATO member.

Officials said ministers will review the transition to full Afghan control of security, with 75 percent of the population now safeguarded by local forces.

Insider attacks -- the killing of NATO soldiers by renegade Afghan troops -- are a cause of "deep concern," one official said, while stressing that the suspension of joint operations in response had been only temporary and limited.

Some 53 NATO soldiers have been killed in 'insider attacks' so far this year, the official said, up from the 51 previously given.

US Defense Secretary Leon Panetta will attend the two-day talks after making critical remarks of Afghan President Hamid Karzai for not fully acknowledging the sacrifices NATO troops have made, with US deaths alone now more than 2,000.