Fox News national security correspondent Jennifer Griffin reported the latest this morning on a significant escalation in the war in Syria, as Russian forces begin airstrikes in the country's north in support of the Assad regime. 

Griffin said a three-star general from Russia delivered a request - known as a "demarche" - to a U.S. military attache in Baghdad, asking that U.S. planes clear out of the area.

U.S. fighter jets will not comply with the request and U.S. bombing missions continued today, Griffin reported. One senior official characterized the exchange at the embassy as "heated."

The strikes occurred near Homs, roughly 60 miles east of a Russian naval facility in Tartus.

Griffin said that ISIS is not known to be operating in that area. Rather, it's a hub for the Free Syrian Army. 

Russia's defense minister says the bombings are aimed at ISIS positions.

Griffin said that "clearly" President Obama was not told about these airstrikes during his Monday meeting with Vladimir Putin.

Watch her full report above and stay tuned to Fox News for the latest developments.