After the United States shot down a Syrian military SU-22 over Syria on Sunday, the United States, Russia, and Iran have begun establishing “red lines” for one another, or borders within the nation each respective state’s military assets cannot cross without being engaged as a hostile.

While the establishment of red lines is not a new development in the ongoing conflict with the Islamic State within Syria, the decision to reestablish and reinforce these lines speaks directly to the heightened tensions between external forces and the groups they support within Syria.

Russia issued a warning to the United States after the American F/A-18 Super Hornet shot down the Syrian SU-22 declaring that any U.S. aircraft seen flying west of the Euphrates River would now be seen as hostile, and engaged with Russian anti-aircraft defenses.

Over the weekend, Iran launched a volley of ballistic missiles at ISIS targets within Syria, marking the first such Iranian offensive in decades.  Six missiles with a maximum range of approximately 435 miles were fired from the western region of Iran, flying through Iraqi airspace, before impacting their targets in Deir ez-Zor.

“This attack, before being a message for the terrorists, is a message for the supporters of terrorism in the region which are symbolized by the Saudi regime and the Americans,” the state television website quoted Iranian parliamentarian Javad Karimi Qoddousi as saying.

The United States was forced to shoot down an armed drone over Syria last week after it attacked coalition backed fighters, and it is believed the drone belonged to the Iranian military.

Iran’s increased involvement in Syria speaks not only to their commitment to their alliance with Bashar al Assad’s Syrian government, but also to their intent to secure a land corridor to its allies in Iraq, Syria, and Lebanon through contested Syrian territory.  Allowing Iran to establish a “Shi’ite crescent” of influence throughout the region has long troubled the United States and its allies, but it remains unclear just how far American-backed forces would be willing to go in order to prevent such a development.

Both the Syrian and Iranian governments have now publicly accused the United States of working in support of the Islamic State, as the U.S. has been forced to engage Pro-Syrian forces on four separate instances in recent weeks as they’ve advanced on, or attacked, U.S. backed fighters.  In Sunday’s incident, for instance, Syria claimed their jet was conducting anti-ISIS operations, despite there being no ISIS presence in the region as it dropped its bombs (on U.S. backed rebels).