Nato is set to approve the deployment of Patriot missile interceptors to defend Turkey's border with Syria.
A meeting of the 28-member alliance's foreign ministers in Brussels follows a request from Turkey to boost its defences along the border, the BBC reports.
Nato officials have made clear such a move would be purely defensive.
The interceptors, if approved, could be used to shoot down any Syrian missiles or warplanes that stray over the border.
The BBC's defence correspondent says a Nato team has already visited a number of sites in Turkey in preparation for the deployment of Patriot batteries.
Earlier, United States President Barack Obama warned Syrian President Bashar al-Assad he would face "consequences" if he uses chemical weapons against his people.
"The world is watching. The use of chemical weapons is and would be totally unacceptable," he said in a speech at the National Defense University in Washington.
"If you make the tragic mistake of using these weapons there will be consequences and you will be held accountable."
A Syrian official has insisted it would "never, under any circumstances" use such weapons, "if such weapons exist".
US officials say there are signs of chemical weapon components having been moved in recent days in Syria.