* Israel facing growing pressure over civilian deaths * Tunnel destruction a main goal of Israeli ground offensive * U.N. outraged over refugee deaths at Gaza shelter * Palestinian deaths exceed 1,400; 59 Israeli dead (Adds new deaths, soldiers wounded by mortar, White House remarks) By Nidal al-Mughrabi and Maayan Lubell GAZA/JERUSALEM, July 31 (Reuters) - Israeli Prime Minister Benjamin Netanyahu, facing international alarm over a rising civilian death toll in Gaza, said on Thursday he would **t accept any ceasefire that stopped Israel completing the destruction of militants' infiltration tunnels. The Israeli military estimated on Wednesday that accomplishing that task would take several more days, extending a four-week-old aerial and ground offensive in the small, densely populated coastal territory. "I wont agree to any proposal that will **t enable the Israeli military to finish this important task, for the sake of Israel's security." Leaving open the option of widening its ground campaign in the Islamist Hamas-dominated Gaza Strip, the Israeli military said it had called up an additional 16,000 reservists.