Russian violations of Turkish airspace are "unacceptable", NATO chief Jens Stoltenberg said Monday, calling an emergency meeting of alliance countries to discuss the crisis around a key member state.

"Russia’s actions are not contributing to the security and stability of the region," Stoltenberg said after a meeting with Turkish Foreign Minister Feridun Sinirlioglu in Brussels, after Turkey said its jets intercepted a Russian fighter near the Syrian border at the weekend.