Turkey has agreed to host an early warning radar as part of Nato's missile defence system aimed at countering ballistic missile threats from neighbouring Iran, the Turkish Foreign Ministry said.
The ministry said discussions on Turkey's contribution to the alliance missile defence shield had reached "their final stages".
It did not say when or where the US early warning radar would be stationed.
Nato members agreed to an anti-missile system over Europe to protect against Iranian ballistic missiles at a summit in Lisbon last year.
A compromise was reached with Turkey, which has cultivated close ties with its neighbour Iran and had threatened to block the deal if Iran was explicitly named as a threat.
Under the Nato plans, a limited system of US anti-missile interceptors and radars already planned for Europe - to include interceptors in Romania and Poland as well as the radar in Turkey - would be linked to expanded European-owned missile defences.
That would create a broad system that protects every Nato country against medium-range missile attack.
Turkey has built close economic ties with Iran and has been at odds with the US on its stance toward Iran's nuclear programme, arguing for a diplomatic solution to the stand-off instead of sanctions.
But the agreement over hosting the radar comes at a time when Turkey and Iran appear to be differing on their approach towards Syria, with Turkey becoming increasingly critical of Iranian ally Syria's brutal suppression of anti-regime protests.
The Foreign Ministry made no mention of Iran. It said the system would strengthen both Nato and Turkey's own defence capacities.
Russia opposes the planned system, which it worries could threaten its own nuclear missiles or undermine their deterrence capability.
Russia agreed to consider a Nato proposal last year to co-operate on the missile shield, but insisted the system be run jointly. Nato rejected that demand and no compromise has been found yet.