In addition to violating Turkey’s airspace at least twice on Monday, Russian aircraft flew alarmingly close to American aircraft engaged in anti-ISIS operations in Syria this week.

“The closest has been within a handful of miles of our remotely piloted aircraft,” Lt. Gen. Charles Brown explained to CBS. “But to our manned aircraft they’ve not been closer than about 20 miles.”

Brown remains optimistic about the clashing air campaigns. He believes Russia will not force out the American planes in Syria.

“We’re up a lot more often than [the Russians] are so when we do have to move around [them] for safe operation, it’s for a small period of time compared to the hours and hours that we’re airborne over Iraq and Syria,” he said.

Russia, a longtime ally of Syrian President Bashar al-Assad, violated NATO-member Turkey’s airspace twice on Monday. Russia Today reported that the first incident occurred because of bad weather. Ironically, the excuse came just as a weather forecaster on Rossiya 24 informed her audience the weather in Syria is ideal for an airstrike campaign.

However, NATO and Turkey condemned Russia after their planes flew into the airspace a second time. Turkish President Recep Tayyip Erdoğan warned Russia the continuing violations could eventually mean the nation will “lose Turkey” as an ally. The country joined the fight against the Islamic State (ISIS/ISIL) in Syria over the summer. They remained hesitant for over a year due to their dislike of Assad.

“An attack on Turkey means an attack on NATO,” he declared. “Our positive relationship with Russia is known. But if Russia loses a friend like Turkey, with whom it has been cooperating on many issues, it will lose a lot, and it should know that.”

NATO chief Jens Stoltenberg told the Associated Press that “[I]t’s unacceptable to violate the airspace of another country.” A Russian MIG-29 “harassed” at least eight Turkish F-16 jets on Turkey’s border with Syria. Spokesperson Carmen Romero confirmed that Stoltenberg will speak with Russia about the violations.

“Nato has issued a stern ultimatum,” continued Erdoğan. “We cannot endure it. Some steps that we do not desire are being taken. It is not suitable for Turkey to accept them. This is also beyond the principles of Nato.”

Two other violations occurred over the weekend. “It doesn’t look like an accident, and we’ve seen two of them over the weekend,” said Stoltenberg.

The U.S. also reached out to Moscow about the planes. They hope Russian officials will meet with them and provide a legitimate reason for flying into Turkey.

“We await a response from them and we expect a response from them,” stated Secretary of Defense Ash Carter. “It’s only professional that you follow through on the request they made and they’ve not done that yet, and that may be a further sign of their strategic confusion.”