The United States, France and Britain told NATO envoys on Saturday their coordinated air strikes on Syrian government targets overnight were a last resort and aimed to stop more chemical attacks, the alliances chief said. The three allies briefed NATO ambassadors at a special session at the alliance headquarters and won support from the other 26 NATO members, who sought more diplomatic pressure to uphold an international ban on poison gas attacks like the one the West believes Syria conducted on April 7 in Douma.