The White House on Monday said it will defend American-backed rebels in Syria with airstrikes if necessary, signaling deeper involvement in the country's brutal four-year civil war, according to AFP.
President Barack Obama's administration said it will take "additional steps" to defend U.S. trained and equipped forces, warning Bashar Al-Assad's regime "not to interfere."
"The President approved this recently upon the recommendation of his senior military advisors," a senior administration official told AFP.
White House spokesman Josh Earnest said Assad's regime had not so far hampered U.S.-backed forces, but he nonetheless raised the possibility of strikes against it should the need arise.
The United States, Earnest said, was "committed to using military force where necessary to protect the coalition-trained and equipped Syrian opposition fighters."
The decision was taken under a 2001 rule authorizing the use of military force against terror groups, which critics say has already been stretched too far.
Officials argue that authority includes the ability to provide "defensive fires support."
The White House thus confirmed a report on Sunday that Obama had authorized the use of airstrikes to defend U.S.-trained Syrian rebels if they come under attack from terrorist groups or the Assad regime.
The United States has trained and equipped a number of fighters — screened and determined to be "moderate" — to operate against the jihadist Islamic State (ISIS) organization.
Monday's announcement came as diplomatic efforts to halt the carnage in Syria resume.
An estimated 140,000 people have died in the conflict, which began as an uprising against the Assad regime but has morphed into a multipronged religious and ethnic civil war.
A UN envoy recently presented his plan to resuscitate failed talks and foreign ministers from the United States, Russia and Saudi Arabia held talks in Qatar on Monday.
The trio agreed to the "need for a meaningful political transition" according to State Department spokesman Mark Toner.
Lavrov, however, later condemned Washington's move toward a more robust involvement in Syria.
"We believe it's counterproductive to announce publicly that some U.S.-trained armed groups… will be under the protection of the coalition's air forces," Lavrov said.
Separately on Monday the Treasury Department imposed sanctions on seven entities and four individuals, and named seven vessels as blocked property.