"We must be prepared for a prolonged campaign," Xinhua quoted Israeli Prime Minister Benjamin Netanyahu saying at a joint televised press conference with Defence Minister Moshe Ya'alon and Chief of Staff Lt.Gen. Benny Gantz.
"The campaign will not end until we neutralise the tunnels whose sole purpose is killing our citizens. ... We will continue to act with force and discretion until our mission is accomplished," he said, adding that any ceasefire agreement will have to include "the disarming of terror organisations and demilitarisation of the Gaza Strip".
Earlier Monday night, the Israeli military said that Gaza militants attempted to infiltrate into Israel from the northern Gaza Strip through a cross-border tunnel.
Israeli media reported casualties among the Palestinian forces. A few hours earlier, a Gaza mortar shell reportedly killed four people in the regional council of Eshkol in Israel's Southern District and wounded 17 more.
Hamas took responsibility for the fire. Netanyahu's speech shattered any hope of a swift end to the 21- day-long raging conflict between Israel and the Islamist Hamas movement, which so far has claimed the lives of more than 1,050 Palestinians, over 70 percent being civilians, and 50 Israelis.