The U.S. called on Russia to respect Turkey's airspace late Saturday following Turkish claims a Russian warplane crossing its southern border."The United States joins NATO in standing in solidarity with Turkey and we call on Russia to respect Turkish airspace and cease activities that risk further heightening instability in the region," Pentagon spokesman Mark Wright said.On Saturday, Turkey's Foreign Ministry said a Russian SU-34 bomber jet had been repeatedly warned on Friday after it violated NATO member Turkey's airspace.The Turkish Air Force raised the alert levels on bases around the country following the incident, Turkish military sources said.Russia's Defense Ministry denied crossing into Turkish airspace.NATO Secretary General Jens Stoltenberg also called on Russia to respect Turkish airspace.Turkey's President Recep Tayyip Erdoğan said officials had contacted Russia to arrange a meeting with Russian President Vladimir Putin to discuss the incident but had yet to receive a response.Russian jets have violated Turkish airspace several times since Moscow deployed military forces to Syria in late September.On Nov. 24, Turkish F-16 fighters on aerial patrol intercepted and shot down a Russian SU-24 bomber jet after it ignored warnings and crossed into Turkish airspace, leading to heightened tensions between Moscow and Ankara.