American military officials have accused Russian fighter jets of harassing American drones over Syria for the third consecutive day. Tensions between the two countries are common in Syria as both conduct patrols on the ground and in the air. The US military claims that the encounter on Friday lasted for two hours, during which three MQ-9 drones were subjected to “unprofessional close passes” by Russian aircraft. Russia and Syria have also begun a six-day joint training exercise. Russian Rear Adm. Oleg Gurinov stated that Moscow is concerned about the flights of US-led coalition drones over northern Syria, citing them as “systematic violations of protocols.” This friction comes after Russian military aircraft reportedly engaged in unsafe behavior earlier in the week. The US and France are part of an international coalition fighting ISIS in Syria. Meanwhile, Russia has been involved in the Syrian conflict since 2015, supporting President Bashar Assad’s forces. The US military has called on Russia to return to professional norms so that the focus can be on defeating ISIS. However, the Russian officer warned that the increase of coalition drones’ uncoordinated flights could lead to escalation, adding that Russia is not responsible for their safety.