In Washington, State Department spokesman John Kirby said "We're looking at the full range of options here and those comments notwithstanding, we still have a responsibility as a government to consider all those options."
"I don't find them (comments like the warning) helpful to moving forward, to reach some sort of diplomatic solution here. But the Russians should speak for themselves and why they're saying that kind of thing," he said.
Russia responded with dismay to the U.S.-led coalition's air raid on Syrian army positions near Deir el-Zour that killed 60 Syrian soldiers on Sept. 17, rejecting the U.S. explanation that the attack was a mistake.
Konashenkov said "we have taken all the necessary measures to prevent any such 'mistakes' with regard to Russian servicemen and military facilities in Syria."
He said the range of Russia's S-300 and S-400 air defense missile systems deployed to Syria would be a "surprise" to any country operating its aircraft over the country. Konashenkov added that the Syrian army also has various Soviet- and Russian-built air defense missile systems, which have undergone modernization over the past year.
Since Russia has launched its air campaign in Syria in support of Assad's forces a year ago, the Russia and the U.S. militaries have maintained contacts to prevent any midair incidents between Russian warplanes and the aircraft from the U.S.-led coalition in the skies over Syria.
Konashenkov warned, however, that the Russian military won't have time to use the hotline if it sees missiles on their way to targets in Syria.
"It must be understood that Russian air defense missile crews will unlikely have time to clarify via the hotline the exact flight program of the missiles or the ownership of their carriers," he added.
In an apparent hint at the U.S. stealth aircraft, he added that any "dilettante illusions about stealth planes could collide with disappointing realities."
The Russian military announced Tuesday that a battery of the S-300 air defense missile systems had been sent to Syria to protect a Russian facility in the Syrian port of Tartus and Russian navy ships off the Mediterranean coast.
Tartus is the only naval supply facility Russia has outside the former Soviet Union.
The deployment has added more punch to the Russian military force in Syria, which already includes long-range S-400 missile defense systems and an array of other surface-to-air missiles at the Hemeimeem air base in Syria's coastal province of Latakia.
Russia has conducted an air campaign in support of Assad since Sept. 30, 2015, saving his army from imminent defeat and helping it win key ground.
Matt Lee in Washington contributed to this report.