BRUSSELS—The North Atlantic Treaty Organization urged “calm and de-escalation” in the wake of Turkey shooting down of a Russian jet fighter.

Speaking after an emergency meeting of alliance ambassadors, Jens Stoltenberg, the NATO secretary general, said the alliance has repeatedly expressed solidarity with Turkey over violations of its airspace.

“This highlights the importance of having and respecting arrangements to avoid such incidents in the future,” Mr. Stoltenberg said. “As we have repeatedly made clear, we stand in solidarity with Turkey and support the territorial integrity of our NATO Ally, Turkey.”

The NATO statement came after the Turkish military shot down a Russian aircraft that Turkish and Western officials said had entered its airspace.

U.S. officials confirmed the Russian plane briefly crossed into Turkey. Mr. Stoltenberg confirmed that other allies had provided information that backed the Turkish account of the incident.