(Reuters) - NATO says the system is intended to defend the alliance, at odds with Iran over its suspicions Tehran is developing nuclear weapons, against possible missile attack by "rogue states."
Turkey, which has strengthened ties with neighbors Iran and Syria in recent years, has said it is not opposed to the idea of a defense shield in Europe. But it has expressed concerns that the system might be regarded as hostile by Iran if the alliance lists the Islamic Republic as a threat.
NATO Secretary General Anders Fogh Rasmussen said last week there was broad agreement among NATO member states about the need for a missile defense system, which will be discussed at a summit in Lisbon on November 19-20.
NATO operates by consensus and needs approval of its 28 members.
Defense Secretary Robert Gates held talks with Turkish officials last week on the sidelines of a NATO meeting.
"There were negotiations on the issue in Brussels last week, and the final decision is to be made in the Lisbon summit," a Turkish Foreign Ministry official told Reuters.
"Within this frame, we do not lean toward the idea of defining countries like Iran, Syria and Russia as threats. The minister has conveyed our opinion on the subject."
On Friday, Turkey's Foreign Minister Ahmet Davutoglu said:
"We do not perceive any threat from any neighbor countries and we do not think our neighbors form a threat to NATO."
Turkey's Defense Minister Vecdi Gonul has said Ankara was also seeking an agreement on technical issues, including how the NATO-wide shield system would affect Turkey's missile system and if it would cover the entire country.
Turkey observers say the shield system illustrates Ankara's increasingly difficult balancing act in keeping good ties with long-time Western allies and its new friends.
A long-time NATO member that aspires to join the European Union, Turkey has boosted ties with Iran and other Muslim countries since Prime Minister Tayyip Erdogan's AK Party took office, raising fears in some circles of a "change of axis" to become less West-facing.
Turkey irritated the United States when it announced that along with Brazil it had struck a deal with Iran to ease a standoff over accusations it is developing nuclear weapons -- something Tehran denies. Turkey later voted against United Nations sanctions against the Islamic Republic.
"If this NATO project gets widespread support in NATO, Turkey could easily end up having to choose between the alliance and Iran," Semih Idiz, a foreign policy expert who writes for liberal daily Milliyet wrote last week.
A NATO official in Brussels told Reuters the shield was not deployed against any specific country.
"We are in a situation where more than 30 countries are building ballistic missiles and in 10 years or 12 years we will be in a different global or international situation," the official said.