NATO does not expect to formally join the US-led coalition fighting the Islamic State group in Syria and Iraq, even if it will cooperate on a practical and "niche" level, the US ambassador to the alliance said Wednesday.

"We're not hung up on being declared a member or not. We're simply interested in practical support," Douglas Lute said ahead of a meeting of NATO foreign ministers in Brussels on Thursday and Friday.

In April US President Barack Obama told an audience in Germany that Washington needed "a strong Europe to bear its share of the burden" in the fight against the Islamic State jihadists.

US Defense Secretary Ashton Carter said in February -- also at a NATO meeting in Brussels -- that the 28 alliance members were exploring the possibility of NATO becoming a member of the anti-IS coalition itself.

Lute said the ministers meeting in Brussels will "ask the more practical question of, are there ways .. in capacity support and other niche capabilities .. that we can contribute?"

NATO Secretary General Jens Stoltenberg said: "We will discuss what more NATO can do to support Iraq. We are already training several hundred Iraqi officers in Jordan.

"We have received a request from (Iraqi) Prime Minister al-Abadi to expand our training mission into Iraq itself. And we will consider this request," added the NATO chief.

The US ambassador also broached the possibility of training missions or support for the defence sector or army reform in Libya -- if the new government asks for it -- or in Tunisia.

NATO's AWACS monitoring aircraft could also help provide intelligence about what is happening in the skies over Iraq or Syria -- even if they only remain over Turkey, according to a diplomatic source.

Lute said that at this stage the anti-IS coalition does not need the alliance AWACS to be deployed in Syrian or Iraqi airspace, a prospect which would cause concern in certain European capitals.