the US does not know, but israel does. Israel knows or should know, if the assertion is true. if it's true, to me it's like the missles in Cuba during the missle crisis. Lebanon, get them out of there, or Israel will. i suspect it's true, and that syria, leb and Hizbola see it as a deterrent against Israel counterattack for terrorist acts, revenge for Mugnibyah killing, revenge for Israel blowing up Syrian nuc site. could get ugly. and if it does, damascus will get it this time, along with lebanon. of course, so will israel, so noone wins.
U.S., allies stage 20 strikes against Islamic State in Iraq (Reuters)
from the article: State Dept.: U.S. unsure whether Syria sent missiles to Hezbollah