NATO leaders will launch a new Europe-wide ballistic missile shield at a Lisbon summit but will not openly identify Iran as a threat so as to win over Turkey, officials said Thursday.

US President Barack Obama and supporters of the shield want to wrap up broad agreement at the Friday-Saturday summit on a missile umbrella stretching across European members of the 28-nation alliance.

Turkey is mindful of its delicate position with neighbouring Iran, however, and has said it will refuse to sign up to a NATO document that names Iran as the threat in the final declaration.

Diplomats said there had been intense debate in the run-up to the summit about whether Iran should be targetted as a specific menace in the public document they adopt.

On the eve of the tightly secured Lisbon talks, however, an official at French Elysee presidential office in Paris told reporters that Iran will not figure as a missile threat in the public declaration.

"This will not figure in those words in the document that we are to adopt," the official said, speaking on condition of anonymity. "We will not put the origin of the emerging menace in black and white in the documents to be adopted."

The French official did not give a reason for omitting a mention of Iran from the NATO document, but Turkish President Abdullah Gul had said 10 days ago that identifying Iran "is wrong and will not happen."

Even if Iran is left out of the final declaration, allies were still debating Thursday whether to mention Iran in a list of countries identified in a confidential threat assessment, a NATO diplomat said on condition of anonymity.

"Certain countries are uncomfortable with naming their neighbours," a senior US official said this week.

NATO Secretary General Anders Fogh Rasmussen told reporters on Monday that there was "no reason to name specific countries."

"The fact is that more than 30 countries have, or are aspiring to get missile technologies with a range sufficient to hit targets in the Euro-Atlantic area," he said.

NATO wants to link existing or future national missile defence systems to create an umbrella that would protect all of Europe's population and territory, at a cost of less than 200 million euros, officials say.

Russian President Dmitry Medvedev, who will meet here Saturday with NATO leaders for the first time since waging a war with Georgia in 2008, has fought against the missile shield as a menace to its own nuclear deterrence.

NATO leaders plan to defuse this opposition by inviting Russia to join the defence shield, extending its protection across Russian territory.

"We are trying to find the language that makes it clear that this is not about Russia, which is pretty easy by saying we're going to ask Russia to cooperate with us," the senior US official said.

"There is no doubt that there is a growing threat. Missiles are proliferating," he added.

Rasmussen has said he expects Russia and NATO to launch a study of Russia's possible inclusion in the missile defence system, which would be a remarkable turnaround after years of outright opposition by Moscow.