US Fears New Massacre in Syria UN observers blocked from town of Haffa By Rob Quinn, Newser Staff Posted Jun 12, 2012 4:22 AM CDT 13 comments Comments Smoke rises from Syrian government attacks on the town of Rastan, in Homs province. (AP Photo/Shaam News Network via AP video) (Newser) – The US and UN are warning that the Syrian government may be organizing another massacre, this time in the town of Haffa, where UN monitors have been impeded, reports the BBC. International envoy Kofi Annan says he is "gravely concerned" about the escalation of violence, and reports of mortar, tank, and helicopter attacks on Haffa and its surrounding villages. "A large number of civilians are trapped in these towns," he warned. The Syrian regime is using "new horrific tactics" on rebellious areas, a State Department spokeswoman says, warning: "People will be held accountable." A new UN reports has, for the first time, placed the Syrian government and its allied militias on a list of groups that kill and sexually attack children, AP reports. The report found that in Syria, children as young as nine have been the victims of killing, torture, sexual violence, and arbitrary detention, and have been used as human shields.