The militant group is considering targeting Israeli Prime Minister Ariel Sharon in retaliation for the killing of Hamas spiritual leader Sheikh Ahmed Yassin, another top Hamas official said. The Islamic group made veiled threats it would retaliate against Washington over Yassin’s killing, although it has rarely attacked US targets during the conflict between the Palestinians and Israel. Hamas’s armed wing issued a statement on Monday saying Washington’s backing of Israel had made Yassin’s assassination possible. “All the Muslims of the world will be honoured to join in the retaliation for this crime,” the statement said. US President George W. Bush said after the statement that Washington takes the threat seriously. On Tuesday, the State Department repeated its warning for Americans not to travel to the Gaza Strip.