UN Secretary General Ban Ki-moon expressed concern about the recent escalation of hostilities between Israel and Hamas in the wake of Israeli killing of four Palestinians in Gaza, his spokesman Martin Nesirky told the daily press briefing. "The Secretary General calls on all to refrain from violence and exercise restraint. All should abide by the November 2012 understanding on a ceasefire, " Nesirky said in answer to a question. He added that the UN is also "concerned about the humanitarian consequences of a deterioration of the situation" between the two sides. The four Palestinians were killed when an Israeli aircraft bombed what Israel called the "terror tunnel" into Israel, used by Hamas, which rules Gaza since it won the elections in 2006