"NATO allies have expressed strong condemnation of this completely unacceptable act," NATO Secretary-General Anders Fogh Rasmussen said after the gathering.

Rasmussen said NATO security was "indivisible", but he said NATO's Article 5, which calls for member states to see an attack on one country as an attack on all the alliance's members, had not been discussed.

"We stand together with Turkey in spirit of solidarity," he said.

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