Pentagon sources said finalized plans include types and numbers of forces, no-fly zone protection, limited air strikes, and safeguarding chemical and biological sites.
Timeline information wasn't indicated. Intervention could come anytime.
Earlier reports said insurgents have Libya-supplied chemical weapons. Others falsely accused Assad of using them in Deraa, Hama and Idlib.
Spurious accusations give Washington greater pretext to intervene. Western chemical attacks could be blamed on him.
US naval forces are "maintaining a presence of three surface combatants and a submarine in the easter Mediterranean. They're conducting "electronic surveillance and reconnaissance...."
On June 15, The New York Times headlined "Russia Sending Missile Systems to Shield Syria," saying:
"Russia's chief arms exporter said Friday that his company was shipping advanced defensive missile systems to Syria that could be used to shoot down airplanes or sink ships if the United States or other nations try to intervene to halt the country's spiral of violence."
On Friday, Rosoboronexport general director Anatoly Isaykin said:
"I would like to say these mechanisms are really a good means of defense, a reliable defense against attacks from the air or sea."
"This is not a threat, but whoever is planning an attack should think about this."
Moscow military analyst Aleksander Golts said weapons shipments warn Western countries against intervening.
"Russia uses these statements as a form of deterrence in Syria. They show other countries that they are more likely to suffer losses."
Weapons sent include:
- Pantsyr-Si radar-guided missile and artillery systems able to hit high-altitude aircraft up to 12 miles away;
- Buk-M2 antiaircraft missiles capable of higher altitude strikes up to 82,000 feet at longer ranges; and