Syria said Sunday it is still negotiating with the Arab League over the bloc's request to send observers into the country, as tightening sanctions by Arab and other nations fail to halt the eight-month crackdown on anti-government protesters. New violence killed at least six people on Sunday, including a female university professor and a father and his three children in central Syria, opposition activists said. Arab leaders have given Syria a new deadline of Sunday to respond to the League's peace plan, which calls for the admission of observers to ensure compliance with government cease-fire. They also held out the threat of pushing for U.N. involvement if Syria balks.