Washington:  The United States and its Nato allies are close to an agreement to erect a missile shield over Europe, a project that would give the military alliance a fresh purpose while testing President Barack Obama's campaign to improve relations with Russia.

The deal is likely to be sealed at a two-day Nato summit starting Friday in Lisbon, Portugal, officials say, as part of what the alliance calls its new "strategic concept," the first overhaul of its basic mission since 1999.

The summit will include Obama and leaders of the 27 other member countries of the North Atlantic Treaty Organisation. Russian President Dmitry Medvedev will join a separate Nato-Russia session on Saturday.

Outlines of the deal were provided to The Associated Press by American officials who spoke on condition of anonymity to discuss internal allied deliberations.

Under the arrangement, a limited system of US anti-missile interceptors and radars already planned for Europe would be linked to expanded European-owned missile defences. That would create a broad system that would protect every Nato country against medium-range missile attack.

Nato plans to invite Russia to join the missile shield effort, although Moscow would not be given joint control. The gesture would mark a historic milestone for the alliance, created after the Second World War to defend Western Europe against the threat of an invasion by Soviet forces.

The Bush administration first proposed stationing 10 interceptor missiles in Poland and an advanced radar in the Czech Republic, saying the system was aimed at blunting future missile threats from Iran.

Russia was furious, saying the missiles threatened the deterrent value of its nuclear arsenal. At one point Moscow warned that if the plan went forward, it would station missiles close to Poland.

The Obama administration cancelled the original plan in September 2009, proposing instead a reconfigured missile shield that would begin with ship-based interceptors and radars, followed by more advanced land-based interceptors to be deployed in Romania by 2015 and Poland by 2018. This is to be the core US contribution to Nato's European missile defense system.

Hesitation

The United States has asked Turkey, also a member of Nato, to host some of the radar defences and to approve the proposal for a Europe-wide defence network. Turkey has hesitated, saying it does not want the system explicitly to target its neighbour, Iran.

US officials close to pre-summit talks were optimistic that the proposed European missile shield's remaining obstacles could be overcome. They said Russia seems to be seriously considering Nato's plan, while Turkey's concerns could be finessed.

"The Russians seem to be playing ball and seem to be somewhat open-minded about this," said F. Stephen Larrabee, a specialist in European security issues at the Rand Corp think tank.

In Larrabee's view, Nato must still convince Moscow that the planned system will not undermine the credibility of Russia's nuclear arsenal.