ISTANBUL (AFP) - Turkish Prime Minister Recep Tayyip Erdogan said on Saturday it was "unthinkable" for Ankara to normalise relations with Israel until it apologised over its bloody raid on a Turkish ship heading for Gaza. "As long as Israel does not apologise to Turkey, pay compensation to the families of the victims and lift its blockage on the Gaza strip, a normalisation of relations is unthinkable," he said at the opening of a meeting of Palestinian ambassadors. Erdogan accused Israel of perpetrating a "barbaric massacre" and "shooting in the back" the nine unarmed Turkish activists killed when Israeli commandos stormed a Turkish ferry leading a flotilla which was attempting to break Israeli's naval embargo on Gaza in May 2010.