Israeli police Sunday sought a motive in the stabbing deaths of six family members, including two children, authorities in Rishon Lezion said.

Found dead in their apartment Saturday were Eduard and Ludmilla Ushrenko, both 56; their son Demetri, 32; his wife Tatiana, 28; and their two

children, Revital, 3, and Netanel, 4 months, The Jerusalem Post reported Sunday.

Someone set fire to the apartment after killing the family, Ynetnews.com reported. Police said they doubted neighbors' claims that no one heard or saw anything suspicious.

"Someone had to have seen a car approaching, or heard a scream - something out of the ordinary," an unnamed source close to the investigation told Ynetnews.

Prime Minister Binyamin Netanyahu spoke of the killings shortly before his weekly Cabinet meeting Sunday, Haaretz reported.

"I want to express pain and deep shock at the terrible murder," Netanyahu said. "I've asked Internal Security Minister Yitzhak Aharonovitch to keep me updated on the steps of solving the horrible crime."