Palestinian authorities said a grave site discovered at the Nasser hospital, the main medical facility in central Gaza, contained nearly 400 bodies
"From a human rights point of view, I utterly condemn these rocket attacks and more especially I condemn Israel's excessive acts of retaliation," U.N. Commissioner for Human Rights Navi Pillay told journalists in Vienna on Thursday.
"I am extremely concerned by what's happening," she added on the sidelines of a conference.
She also condemned killing of a Palestinian teen, whose body was found in Jerusalem on Wednesday.
"It's despicable but now in turn there's been a kidnapping and killing of a Palestinian youth. This cannot happen. This level of retaliation is excessive and this is what is spawned when governments do not respect the rule of law, when governments themselves resort to excessive forms of retaliation," she said.