50 IDF tanks moved back into northern Gaza early Wednesday, residents and Palestinian security said, as Israel pressed ahead with its Gaza offensive alongside fighting in Lebanon. Aircraft carried out at least three airstrikes as the troops moved in, killing a Hamas operative and wounding five others. Hamas said the men were about to fire a rocket at Israel. The army said forces were operating in northern Gaza as part of a campaign to stop terrorism and rocket barrages at Israel. The military said aircraft targeted three groups of militants who were approaching the troops. Early Wednesday, troops took over rooftops of several houses in northern Gaza, residents said, and Israeli aircraft blasted several houses of Hamas and Islamic Jihad operatives after warning the people to leave. In another tactic, the Palestinian phone company said more than 1,000 residents of the southern Gaza city of Khan Younis received recorded messages from Israel, warning them not to hide weapons or shield terrorists. The residents were apparently picked at random, phone company officials said. The latest incursion came in response to the continued rocket fire from Gaza. Earlier on Tuesday, Palestinian terrorists fired a Kassam rocket at Israel from southern Gaza, moderately wounding a Thai worker in a western Negev community.