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TALLINN, Estonia (AP) — U.S. Secretary of State Hillary Rodham Clinton met with her Estonian counterpart Urmas Paet on Thursday prior to the start of a key meeting of NATO foreign ministers.

Clinton, who landed early Thursday, will spearhead discussions on an American nuclear "umbrella" for Europe and the alliance's core mission for the future when the summit begins later in the day.

NATO leader Anders Fogh Rasmussen has said the alliance's members should commit more to the training mission in Afghanistan, seen as being crucial for a smooth transition of power in the country.

Ministers at the two-day talks are also expected to discuss plans for inviting Bosnia to join the alliance.

Almost 20 years after the collapse of the Soviet Union, the 28-member military organization is in the midst of intense self-examination as it re-evaluates its basic purpose.