Dozens of armed Palestinians have been killed so far in Israel's ground offensive in the Hamas-run Gaza Strip, a military source told media on Saturday several hours after the launch of the operation. "Dozens of terrorists have been killed and dozens of others have been wounded. There are no losses on the Israeli side," the source said on condition of anonymity. Palestinian medics in Gaza were not able to immediately comment on the claim. Earlier, Israel launched ground offensive in Gaza on Saturday after carrying out air strikes in the city which killed hundreds of people and injured thousands others. Israeli troops entered in Gaza from 3 sides, Arab TV reported. Israel aims to "take over" areas in Gaza from where militants have fired rockets into the Jewish state, Prime Minister Ehud Olmert's office said after ground troops entered the enclave. "The Israel Defence Forces (army) is planning to take over rocket launching areas from where rockets have been fired over the past weeks and months," it said in a statement. The goal of the operation include "dealing a hard blow to the Hamas terror infrastructure and changing the security reality in the south over a long period of time," it said. Israeli tanks opened fire on Hamas positions after entering the northern Gaza Strip on Saturday and Hamas forces replied with mortar fire, witnesses told a foreign news agency.