Afghanistan will top the agenda at a NATO defence ministers' meeting this week but Syria will also feature amid mounting fatalities and tensions with alliance member Turkey, officials said Monday.

The ministers will also focus on how NATO, winding down operations in Afghanistan ahead of its combat troop withdrawal in 2014, can get "a bigger bang for its buck," making the best of cuts to defence spending driven by slowing economies.

Syria is not officially on the agenda but NATO diplomats said during a series of press briefings that the subject would inevitably be raised, especially after last week's clashes on the Turkish border prompted strong backing for Ankara.

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

On Afghanistan, ministers meeting on Tuesday and Wednesday will look closely at the transition to full Afghan responsibility for 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.

NATO is just beginning to plan for its advice, training and assistance mission after 2014.

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.

Officials all cited the impact of the economic slump on defence spending, highlighting the need for more common effort to make funds go further and the importance of joint operations and capabilities, as demonstrated in Afghanistan.

NATO agreed at a Chicago summit in May on a "2020" concept which gives a large role to such burden sharing but the issue is fraught with political issues as nations jealously guard sovereignty in the all important matter of defence.

"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 major tie-up between Britain's BAE Systems and EADS, the European aerospace giant, represents a huge pooling of European defence resources but officials said it was not on the agenda although ministers would likely take it up.

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.