Rasmussen met with European foreign and defense ministers. On issues related to the Syrian war, he said there were no plans for a deployment over Syrian airspace.
"We're not speaking of a no-fly zone," he said.
NATO forces last year enforced a no-fly zone over Libya to protect civilians from pro-government forces during civil war there. Rasmussen said NATO may deploy Patriot missiles or other defensive measures along the Turkish border with Syria if requested by Ankara, however.
The situation along the Turkish-Syrian border, he said, was "of great concern" to the alliance.
Turkish forces this year have responded when Syrian mortar fire struck the Turkish side of the border. Any move by NATO forces to support allied Ankara would be a "purely defensive measure to defend Turkey," Rasmussen said.
European governments and Arab alliances last week extended recognition to a Syrian opposition council formed earlier this month in Qatar. French leaders are expected to support the defensive aims of the opposition council.