Reports say U.S. President Barack Obama plans to deploy a small number of special operations forces to Syria to advise rebels.
Unidentified U.S. officials were quoted as saying Obama had authorized fewer than 50 commandos to deploy to northern Syria.
A senior administration official said they will "help coordinate local ground forces and coalition efforts" to counter the Islamic State group.
Officials also said the United States would be sending additional aircraft, including F-15 fighters and A-10s, to Turkey's Incirlik air base.
The U.S. decision comes after Russia escalated its military role in Syria to support Syrian President Bashar al-Assad.
Earlier in the day, Russian Deputy Foreign Minister Sergei Ryabkov said Moscow considered the use of U.S. forces without coordination with Assad's government unacceptable.
Russia has conducted a campaign of air strikes in Syria since September 30, targeting enemies of Assad.
The move was expected to be announced later on October 30, as diplomats from 17 countries are meeting in Vienna to seek ways to end the 4 1/2-year war in Syria.