By Nidal al-Mughrabi CAIRO, July 12 (Reuters) - Israeli attacks killed at least six people in the Gaza Strip on Sunday, including a 9-year-old girl, Palestinian health officials said, as mediators held more talks to safeguard the U.S.-brokered ceasefire. Medics said Israeli gunfire directed at a tent encampment on the eastern side of the Al-Bureij refugee camp in central Gaza killed 9-year-old Tala Abu Matar. The Israeli military said it was not aware of the incident.