GAZA — Israel has threatened to assassinate the Palestinian prime minister if Hamas militants do not release a captured Israeli soldier unharmed, it was reported. The warning was delivered to Palestinian President Mahmoud Abbas in a letter, as Israeli officials considered an offer by Hamas to free Cpl. Gilad Shalit — and Israeli military officials prepared an invasion force for a second major offensive into Gaza, The Australian reported. Hamas political leaders in Gaza — including Palestinian Prime Minister Ismail Haniyeh — had gone into hiding. The proposal to free Shalit was brokered by Egyptian President Hosni Mubarak, The Australian said. He warned Hamas Friday it faces severe consequences if it did not modify its ‘extreme stance,’ and called the conflict a lightning rod for Palestinian vengeance. Shalit’s kidnappers issued new demands, including a halt to Israel’s offensive in Gaza and the release of 1,000 prisoners. The kidnappers did not say they would release Shalit in exchange for their demands being met, The Jerusalem Post reported.