"A human being is not capable of something like that … the murder of infants and children and a woman slaughtered," Abbas said in an interview Monday with Israel Radio.
On Friday night, two attackers broke into a home in Itamar, southeast of Nablus, and killed Udi and Ruth Fogel, their 3-month-old daughter Hadas and sons Elad, 3, and Yoav, 11.
The couple's 12-year-old daughter discovered the deaths when she returned home later that night. Two other brothers went unnoticed by the terrorists and were unharmed.
Abbas said the attack was immoral and inhuman.
The Palestinian president said he had expressed his condolences in a telephone conversation with Israeli Prime Minister Binyamin Netanyahu Saturday and agreed to launch a joint investigation with Israeli security forces.
On Sunday night, Netanyahu met with relatives of the Fogel family.
"This heinous act has led all of us to say 'enough.' The security forces are doing everything they can to find the murderers," Netanyahu said.